fs: optimize mpage_bio_submit()
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From: Borislav Petkov on 29 May 2010 08:50 From: Changli Gao <xiaosuo(a)gmail.com> Date: Sat, May 29, 2010 at 09:19:26AM +0800 > optimize mpage_bio_submit() > > check rw, then initialize bio->bi_end_io. > > Signed-off-by: Changli Gao <xiaosuo(a)gmail.com> > ---- > fs/mpage.c | 4 +--- > 1 file changed, 1 insertion(+), 3 deletions(-) > diff --git a/fs/mpage.c b/fs/mpage.c > index 94ff0d1..632681c 100644 > --- a/fs/mpage.c > +++ b/fs/mpage.c > @@ -85,9 +85,7 @@ static void mpage_end_io_write(struct bio *bio, int err) > > static struct bio *mpage_bio_submit(int rw, struct bio *bio) > { > - bio->bi_end_io = mpage_end_io_read; > - if (rw == WRITE) > - bio->bi_end_io = mpage_end_io_write; > + bio->bi_end_io = rw != WRITE ? mpage_end_io_read : mpage_end_io_write; > submit_bio(rw, bio); > return NULL; ok, can you sincerely tell me that your change makes the code more readable? And have you checked to see what the compiler actually "optimizes"? original code: movq $mpage_end_io_read, %rdx #, tmp65 movq $mpage_end_io_write, %rax #, tmp64 cmpl $1, %edi #, rw cmovne %rdx, %rax # tmp65,, tmp64 movq %rax, 80(%rsi) # tmp64, <variable>.bi_end_io .loc 1 91 0 call submit_bio # your change: movq $mpage_end_io_read, %rdx #, tmp63 movq $mpage_end_io_write, %rax #, iftmp.561 cmpl $1, %edi #, rw cmovne %rdx, %rax # tmp63,, iftmp.561 movq %rax, 80(%rsi) # iftmp.561, <variable>.bi_end_io .loc 1 90 0 call submit_bio # so that change does nothing except obfuscating the source a bit more so that you get more headaches whenever you look at it. -- Regards/Gruss, Boris. -- 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: Changli Gao on 29 May 2010 09:40 On Sat, May 29, 2010 at 8:47 PM, Borislav Petkov <bp(a)alien8.de> wrote: > > ok, can you sincerely tell me that your change makes the code more > readable? And have you checked to see what the compiler actually > "optimizes"? > > original code: > > movq $mpage_end_io_read, %rdx #, tmp65 > movq $mpage_end_io_write, %rax #, tmp64 > cmpl $1, %edi #, rw > cmovne %rdx, %rax # tmp65,, tmp64 > movq %rax, 80(%rsi) # tmp64, <variable>.bi_end_io > .loc 1 91 0 > call submit_bio # > > your change: > > movq $mpage_end_io_read, %rdx #, tmp63 > movq $mpage_end_io_write, %rax #, iftmp.561 > cmpl $1, %edi #, rw > cmovne %rdx, %rax # tmp63,, iftmp.561 > movq %rax, 80(%rsi) # iftmp.561, <variable>.bi_end_io > .loc 1 90 0 > call submit_bio # > > so that change does nothing except obfuscating the source a bit more so > that you get more headaches whenever you look at it. > Oh, I didn't check the asm code. Compiler is smarter than I thought. Thanks for your explaining. -- Regards， Changli Gao(xiaosuo(a)gmail.com) -- 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: Borislav Petkov on 29 May 2010 09:50
From: Changli Gao <xiaosuo(a)gmail.com> Date: Sat, May 29, 2010 at 09:33:02PM +0800 > Compiler is smarter than I thought. Not as much as we would like to though :) -- Regards/Gruss, Boris. -- 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/ |