AIM7 40% regression with 2.6.26-rc1
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From: Zhang, Yanmin on 6 May 2008 01:50 Comparing with kernel 2.6.25, AIM7 (use tmpfs) has more than 40% with 2.6.26-rc1 on my 8-core stoakley, 16-core tigerton, and Itanium Montecito. Bisect located below patch. 64ac24e738823161693bf791f87adc802cf529ff is first bad commit commit 64ac24e738823161693bf791f87adc802cf529ff Author: Matthew Wilcox <matthew(a)wil.cx> Date: Fri Mar 7 21:55:58 2008 -0500 Generic semaphore implementation After I manually reverted the patch against 2.6.26-rc1 while fixing lots of conflictions/errors, aim7 regression became less than 2%. -yanmin -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Matthew Wilcox on 6 May 2008 07:20 On Tue, May 06, 2008 at 01:48:24PM +0800, Zhang, Yanmin wrote: > Comparing with kernel 2.6.25, ???AIM7 (use tmpfs) has ???more than 40% with 2.6.26-rc1 > on my 8-core stoakley, 16-core tigerton, and Itanium Montecito. Bisect located > below patch. > > 64ac24e738823161693bf791f87adc802cf529ff is first bad commit > commit 64ac24e738823161693bf791f87adc802cf529ff > Author: Matthew Wilcox <matthew(a)wil.cx> > Date: Fri Mar 7 21:55:58 2008 -0500 > > Generic semaphore implementation > > > After I manually reverted the patch against 2.6.26-rc1 while fixing lots of > conflictions/errors, aim7 regression became less than 2%. 40%?! That's shocking. Can you tell which semaphore was heavily contended? I have a horrible feeling that it's the BKL. -- Intel are signing my paycheques ... these opinions are still mine "Bill, look, we understand that you're interested in selling us this operating system, but compare it to ours. We can't possibly take such a retrograde step." -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Ingo Molnar on 6 May 2008 07:50 * Zhang, Yanmin <yanmin_zhang(a)linux.intel.com> wrote: > Comparing with kernel 2.6.25, AIM7 (use tmpfs) has more than 40% with > 2.6.26-rc1 on my 8-core stoakley, 16-core tigerton, and Itanium > Montecito. Bisect located below patch. > > 64ac24e738823161693bf791f87adc802cf529ff is first bad commit > commit 64ac24e738823161693bf791f87adc802cf529ff > Author: Matthew Wilcox <matthew(a)wil.cx> > Date: Fri Mar 7 21:55:58 2008 -0500 > > Generic semaphore implementation > > After I manually reverted the patch against 2.6.26-rc1 while fixing > lots of conflictions/errors, aim7 regression became less than 2%. hm, which exact semaphore would that be due to? My first blind guess would be the BKL - there's not much other semaphore use left in the core kernel otherwise that would affect AIM7 normally. The VFS still makes frequent use of the BKL and AIM7 is very VFS intense. Getting rid of that BKL use from the VFS might be useful to performance anyway. Could you try to check that it's indeed the BKL? Easiest way to check it would be to run AIM7 it on sched-devel.git/latest and do scheduler tracing via: http://people.redhat.com/mingo/sched-devel.git/readme-tracer.txt by doing: echo stacktrace > /debug/tracing/iter_ctl you could get exact backtraces of all scheduling points in the trace. If the BKL's down() shows up in those traces then it's definitely the BKL that causes this. The backtraces will also tell us exactly which BKL use is the most frequent one. To keep tracing overhead low on SMP i'd also suggest to only trace a single CPU, via: echo 1 > /debug/tracing/tracing_cpumask Ingo -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Matthew Wilcox on 6 May 2008 08:20 On Tue, May 06, 2008 at 01:44:49PM +0200, Ingo Molnar wrote: > * Zhang, Yanmin <yanmin_zhang(a)linux.intel.com> wrote: > > After I manually reverted the patch against 2.6.26-rc1 while fixing > > lots of conflictions/errors, aim7 regression became less than 2%. > > hm, which exact semaphore would that be due to? > > My first blind guess would be the BKL - there's not much other semaphore > use left in the core kernel otherwise that would affect AIM7 normally. > The VFS still makes frequent use of the BKL and AIM7 is very VFS > intense. Getting rid of that BKL use from the VFS might be useful to > performance anyway. That's slightly slanderous to the VFS ;-) The BKL really isn't used that much any more. So little that I've gone through and produced a list of places it's used: fs/block_dev.c opening and closing a block device. Unlikely to be provoked by AIM7. fs/char_dev.c chrdev_open. Unlikely to be provoked by AIM7. fs/compat.c mount. Unlikely to be provoked by AIM7. fs/compat_ioctl.c held around calls to ioctl translator. fs/exec.c coredump. If this is a contention problem ... fs/fcntl.c held around call to ->fasync. fs/ioctl.c held around f_op ->ioctl call (tmpfs doesn't have ioctl). ditto bmap. there's fasync, as previously mentioned. fs/locks.c hellhole. I hope AIM7 doesn't use locks. fs/namespace.c mount, umount. Unlikely to be provoked by AIM7. fs/read_write.c llseek. tmpfs uses the unlocked version. fs/super.c shtdown, remount. Unlikely to be provoked by AIM7. So the only likely things I can see are: - file locks - fasync -- Intel are signing my paycheques ... these opinions are still mine "Bill, look, we understand that you're interested in selling us this operating system, but compare it to ours. We can't possibly take such a retrograde step." -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Matthew Wilcox on 6 May 2008 12:30
On Tue, May 06, 2008 at 06:09:34AM -0600, Matthew Wilcox wrote: > So the only likely things I can see are: > > - file locks > - fasync I've wanted to fix file locks for a while. Here's a first attempt. It was done quickly, so I concede that it may well have bugs in it. I found (and fixed) one with LTP. It takes *no account* of nfsd, nor remote filesystems. We need to have a serious discussion about their requirements. diff --git a/fs/locks.c b/fs/locks.c index 663c069..cb09765 100644 --- a/fs/locks.c +++ b/fs/locks.c @@ -140,6 +140,8 @@ int lease_break_time = 45; #define for_each_lock(inode, lockp) \ for (lockp = &inode->i_flock; *lockp != NULL; lockp = &(*lockp)->fl_next) +static DEFINE_SPINLOCK(file_lock_lock); + static LIST_HEAD(file_lock_list); static LIST_HEAD(blocked_list); @@ -510,9 +512,9 @@ static void __locks_delete_block(struct file_lock *waiter) */ static void locks_delete_block(struct file_lock *waiter) { - lock_kernel(); + spin_lock(&file_lock_lock); __locks_delete_block(waiter); - unlock_kernel(); + spin_unlock(&file_lock_lock); } /* Insert waiter into blocker's block list. @@ -649,7 +651,7 @@ posix_test_lock(struct file *filp, struct file_lock *fl) { struct file_lock *cfl; - lock_kernel(); + spin_lock(&file_lock_lock); for (cfl = filp->f_path.dentry->d_inode->i_flock; cfl; cfl = cfl->fl_next) { if (!IS_POSIX(cfl)) continue; @@ -662,7 +664,7 @@ posix_test_lock(struct file *filp, struct file_lock *fl) fl->fl_pid = pid_vnr(cfl->fl_nspid); } else fl->fl_type = F_UNLCK; - unlock_kernel(); + spin_unlock(&file_lock_lock); return; } EXPORT_SYMBOL(posix_test_lock); @@ -735,18 +737,21 @@ static int flock_lock_file(struct file *filp, struct file_lock *request) int error = 0; int found = 0; - lock_kernel(); - if (request->fl_flags & FL_ACCESS) + if (request->fl_flags & FL_ACCESS) { + spin_lock(&file_lock_lock); goto find_conflict; + } if (request->fl_type != F_UNLCK) { error = -ENOMEM; + new_fl = locks_alloc_lock(); if (new_fl == NULL) - goto out; + goto out_unlocked; error = 0; } + spin_lock(&file_lock_lock); for_each_lock(inode, before) { struct file_lock *fl = *before; if (IS_POSIX(fl)) @@ -772,10 +777,13 @@ static int flock_lock_file(struct file *filp, struct file_lock *request) * If a higher-priority process was blocked on the old file lock, * give it the opportunity to lock the file. */ - if (found) + if (found) { + spin_unlock(&file_lock_lock); cond_resched(); + spin_lock(&file_lock_lock); + } -find_conflict: + find_conflict: for_each_lock(inode, before) { struct file_lock *fl = *before; if (IS_POSIX(fl)) @@ -796,8 +804,9 @@ find_conflict: new_fl = NULL; error = 0; -out: - unlock_kernel(); + out: + spin_unlock(&file_lock_lock); + out_unlocked: if (new_fl) locks_free_lock(new_fl); return error; @@ -826,7 +835,7 @@ static int __posix_lock_file(struct inode *inode, struct file_lock *request, str new_fl2 = locks_alloc_lock(); } - lock_kernel(); + spin_lock(&file_lock_lock); if (request->fl_type != F_UNLCK) { for_each_lock(inode, before) { fl = *before; @@ -994,7 +1003,7 @@ static int __posix_lock_file(struct inode *inode, struct file_lock *request, str locks_wake_up_blocks(left); } out: - unlock_kernel(); + spin_unlock(&file_lock_lock); /* * Free any unused locks. */ @@ -1069,14 +1078,14 @@ int locks_mandatory_locked(struct inode *inode) /* * Search the lock list for this inode for any POSIX locks. */ - lock_kernel(); + spin_lock(&file_lock_lock); for (fl = inode->i_flock; fl != NULL; fl = fl->fl_next) { if (!IS_POSIX(fl)) continue; if (fl->fl_owner != owner) break; } - unlock_kernel(); + spin_unlock(&file_lock_lock); return fl ? -EAGAIN : 0; } @@ -1190,7 +1199,7 @@ int __break_lease(struct inode *inode, unsigned int mode) new_fl = lease_alloc(NULL, mode & FMODE_WRITE ? F_WRLCK : F_RDLCK); - lock_kernel(); + spin_lock(&file_lock_lock); time_out_leases(inode); @@ -1251,8 +1260,10 @@ restart: break_time++; } locks_insert_block(flock, new_fl); + spin_unlock(&file_lock_lock); error = wait_event_interruptible_timeout(new_fl->fl_wait, !new_fl->fl_next, break_time); + spin_lock(&file_lock_lock); __locks_delete_block(new_fl); if (error >= 0) { if (error == 0) @@ -1266,8 +1277,8 @@ restart: error = 0; } -out: - unlock_kernel(); + out: + spin_unlock(&file_lock_lock); if (!IS_ERR(new_fl)) locks_free_lock(new_fl); return error; @@ -1323,7 +1334,7 @@ int fcntl_getlease(struct file *filp) struct file_lock *fl; int type = F_UNLCK; - lock_kernel(); + spin_lock(&file_lock_lock); time_out_leases(filp->f_path.dentry->d_inode); for (fl = filp->f_path.dentry->d_inode->i_flock; fl && IS_LEASE(fl); fl = fl->fl_next) { @@ -1332,7 +1343,7 @@ int fcntl_getlease(struct file *filp) break; } } - unlock_kernel(); + spin_unlock(&file_lock_lock); return type; } @@ -1363,6 +1374,7 @@ int generic_setlease(struct file *filp, long arg, struct file_lock **flp) if (error) return error; + spin_lock(&file_lock_lock); time_out_leases(inode); BUG_ON(!(*flp)->fl_lmops->fl_break); @@ -1370,10 +1382,11 @@ int generic_setlease(struct file *filp, long arg, struct file_lock **flp) lease = *flp; if (arg != F_UNLCK) { + spin_unlock(&file_lock_lock); error = -ENOMEM; new_fl = locks_alloc_lock(); if (new_fl == NULL) - goto out; + goto out_unlocked; error = -EAGAIN; if ((arg == F_RDLCK) && (atomic_read(&inode->i_writecount) > 0)) @@ -1382,6 +1395,7 @@ int generic_setlease(struct file *filp, long arg, struct file_lock **flp) && ((atomic_read(&dentry->d_count) > 1) || (atomic_read(&inode->i_count) > 1))) goto out; + spin_lock(&file_lock_lock); } /* @@ -1429,11 +1443,14 @@ int generic_setlease(struct file *filp, long arg, struct file_lock **flp) locks_copy_lock(new_fl, lease); locks_insert_lock(before, new_fl); + spin_unlock(&file_lock_lock); *flp = new_fl; return 0; -out: + out: + spin_unlock(&file_lock_lock); + out_unlocked: if (new_fl != NULL) locks_free_lock(new_fl); return error; @@ -1471,12 +1488,10 @@ int vfs_setlease(struct file *filp, long arg, struct file_lock **lease) { int error; - lock_kernel(); if (filp->f_op && filp->f_op->setlease) error = filp->f_op->setlease(filp, arg, lease); else error = generic_setlease(filp, arg, lease); - unlock_kernel(); return error; } @@ -1503,12 +1518,11 @@ int fcntl_setlease(unsigned int fd, struct file *filp, long arg) if (error) return error; - lock_kernel(); - error = vfs_setlease(filp, arg, &flp); if (error || arg == F_UNLCK) - goto out_unlock; + return error; + lock_kernel(); error = fasync_helper(fd, filp, 1, &flp->fl_fasync); if (error < 0) { /* remove lease just inserted by setlease */ @@ -1519,7 +1533,7 @@ int fcntl_setlease(unsigned int fd, struct file *filp, long arg) } error = __f_setown(filp, task_pid(current), PIDTYPE_PID, 0); -out_unlock: + out_unlock: unlock_kernel(); return error; } @@ -2024,7 +2038,7 @@ void locks_remove_flock(struct file *filp) fl.fl_ops->fl_release_private(&fl); } - lock_kernel(); + spin_lock(&file_lock_lock); before = &inode->i_flock; while ((fl = *before) != NULL) { @@ -2042,7 +2056,7 @@ void locks_remove_flock(struct file *filp) } before = &fl->fl_next; } - unlock_kernel(); + spin_unlock(&file_lock_lock); } /** @@ -2057,12 +2071,12 @@ posix_unblock_lock(struct file *filp, struct file_lock *waiter) { int status = 0; - lock_kernel(); + spin_lock(&file_lock_lock); if (waiter->fl_next) __locks_delete_block(waiter); else status = -ENOENT; - unlock_kernel(); + spin_unlock(&file_lock_lock); return status; } @@ -2175,7 +2189,7 @@ static int locks_show(struct seq_file *f, void *v) static void *locks_start(struct seq_file *f, loff_t *pos) { - lock_kernel(); + spin_lock(&file_lock_lock); f->private = (void *)1; return seq_list_start(&file_lock_list, *pos); } @@ -2187,7 +2201,7 @@ static void *locks_next(struct seq_file *f, void *v, loff_t *pos) static void locks_stop(struct seq_file *f, void *v) { - unlock_kernel(); + spin_unlock(&file_lock_lock); } struct seq_operations locks_seq_operations = { @@ -2215,7 +2229,7 @@ int lock_may_read(struct inode *inode, loff_t start, unsigned long len) { struct file_lock *fl; int result = 1; - lock_kernel(); + spin_lock(&file_lock_lock); for (fl = inode->i_flock; fl != NULL; fl = fl->fl_next) { if (IS_POSIX(fl)) { if (fl->fl_type == F_RDLCK) @@ -2232,7 +2246,7 @@ int lock_may_read(struct inode *inode, loff_t start, unsigned long len) result = 0; break; } - unlock_kernel(); + spin_unlock(&file_lock_lock); return result; } @@ -2255,7 +2269,7 @@ int lock_may_write(struct inode *inode, loff_t start, unsigned long len) { struct file_lock *fl; int result = 1; - lock_kernel(); + spin_lock(&file_lock_lock); for (fl = inode->i_flock; fl != NULL; fl = fl->fl_next) { if (IS_POSIX(fl)) { if ((fl->fl_end < start) || (fl->fl_start > (start + len))) @@ -2270,7 +2284,7 @@ int lock_may_write(struct inode *inode, loff_t start, unsigned long len) result = 0; break; } - unlock_kernel(); + spin_unlock(&file_lock_lock); return result; } -- Intel are signing my paycheques ... these opinions are still mine "Bill, look, we understand that you're interested in selling us this operating system, but compare it to ours. We can't possibly take such a retrograde step." -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ |