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From: Stefani Seibold on 20 Apr 2010 14:20
Is the MTD mailing list routed to /dev/null?

It is very sad that nobody gives my a reply.

I ask for a merge for the patch, and if there any reason why not, it
would be great to know. Otherwise i can't fix it.

So again, please merge the path for the huge latency problem.

Am Sonntag, den 18.04.2010, 22:46 +0200 schrieb Stefani Seibold:
> From: Stefani Seibold <stefani(a)seibold.net>
>
> The use of a memcpy() during a spinlock operation will cause very long
> thread context switch delays if the flash chip bandwidth is low and the
> data to be copied large, because a spinlock will disable preemption.
>
> For example: A flash with 6,5 MB/s bandwidth will cause under ubifs,
> which request sometimes 128 KB (the flash erase size), a preemption delay of
> 20 milliseconds. High priority threads will not be served during this
> time, regardless whether this threads access the flash or not. This behavior
> breaks real time.
>
> The patch changes all the use of spin_lock operations for xxxx->mutex
> into mutex operations, which is exact what the name says and means.
>
> I have checked the code of the drivers and there is no use of atomic
> pathes like interrupt or timers. The mtdoops facility will also not be used
> by this drivers. So it is dave to replace the spin_lock against mutex.
>
> There is no performance regression since the mutex is normally not
> acquired.
>
> Changelog:
> 06.03.2010 First release
> 26.03.2010 Fix mutex[1] issue and tested it for compile failure
>
> Signed-off-by: Stefani Seibold <stefani(a)seibold.net>
> ---
> drivers/mtd/chips/cfi_cmdset_0001.c | 131 +++++++++++++++++-----------------
> drivers/mtd/chips/cfi_cmdset_0002.c | 122 ++++++++++++++++----------------
> drivers/mtd/chips/cfi_cmdset_0020.c | 136 +++++++++++++++++-----------------
> drivers/mtd/chips/fwh_lock.h | 6 +-
> drivers/mtd/chips/gen_probe.c | 3 +-
> drivers/mtd/lpddr/lpddr_cmds.c | 79 ++++++++++----------
> include/linux/mtd/flashchip.h | 4 +-
> 7 files changed, 239 insertions(+), 242 deletions(-)


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From: Artem Bityutskiy on 23 Apr 2010 08:10
On Sun, 2010-04-18 at 22:46 +0200, Stefani Seibold wrote:
> From: Stefani Seibold <stefani(a)seibold.net>
>
> The use of a memcpy() during a spinlock operation will cause very long
> thread context switch delays if the flash chip bandwidth is low and the
> data to be copied large, because a spinlock will disable preemption.
>
> For example: A flash with 6,5 MB/s bandwidth will cause under ubifs,
> which request sometimes 128 KB (the flash erase size), a preemption delay of
> 20 milliseconds. High priority threads will not be served during this
> time, regardless whether this threads access the flash or not. This behavior
> breaks real time.
>
> The patch changes all the use of spin_lock operations for xxxx->mutex
> into mutex operations, which is exact what the name says and means.
>
> I have checked the code of the drivers and there is no use of atomic
> pathes like interrupt or timers. The mtdoops facility will also not be used
> by this drivers. So it is dave to replace the spin_lock against mutex.
>
> There is no performance regression since the mutex is normally not
> acquired.
>
> Changelog:
> 06.03.2010 First release
> 26.03.2010 Fix mutex[1] issue and tested it for compile failure
>
> Signed-off-by: Stefani Seibold <stefani(a)seibold.net>
> ---
> drivers/mtd/chips/cfi_cmdset_0001.c | 131 +++++++++++++++++-----------------
> drivers/mtd/chips/cfi_cmdset_0002.c | 122 ++++++++++++++++----------------
> drivers/mtd/chips/cfi_cmdset_0020.c | 136 +++++++++++++++++-----------------
> drivers/mtd/chips/fwh_lock.h | 6 +-
> drivers/mtd/chips/gen_probe.c | 3 +-
> drivers/mtd/lpddr/lpddr_cmds.c | 79 ++++++++++----------
> include/linux/mtd/flashchip.h | 4 +-
> 7 files changed, 239 insertions(+), 242 deletions(-)

Pushed to l2-mtd-2.6.git / master.

--
Best Regards,
Artem Bityutskiy (Артём Битюцкий)

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From: Stefani Seibold on 23 Apr 2010 02:10
Hi Andrew,

David did not respond to my request since more than a month. Can u apply
the patch to linux next?

Thanks,
Stefani

Am Dienstag, den 20.04.2010, 20:16 +0200 schrieb Stefani Seibold:
> Is the MTD mailing list routed to /dev/null?
>
> It is very sad that nobody gives my a reply.
>
> I ask for a merge for the patch, and if there any reason why not, it
> would be great to know. Otherwise i can't fix it.
>
> So again, please merge the path for the huge latency problem.
>
> Am Sonntag, den 18.04.2010, 22:46 +0200 schrieb Stefani Seibold:
> > From: Stefani Seibold <stefani(a)seibold.net>
> >
> > The use of a memcpy() during a spinlock operation will cause very long
> > thread context switch delays if the flash chip bandwidth is low and the
> > data to be copied large, because a spinlock will disable preemption.
> >
> > For example: A flash with 6,5 MB/s bandwidth will cause under ubifs,
> > which request sometimes 128 KB (the flash erase size), a preemption delay of
> > 20 milliseconds. High priority threads will not be served during this
> > time, regardless whether this threads access the flash or not. This behavior
> > breaks real time.
> >
> > The patch changes all the use of spin_lock operations for xxxx->mutex
> > into mutex operations, which is exact what the name says and means.
> >
> > I have checked the code of the drivers and there is no use of atomic
> > pathes like interrupt or timers. The mtdoops facility will also not be used
> > by this drivers. So it is dave to replace the spin_lock against mutex.
> >
> > There is no performance regression since the mutex is normally not
> > acquired.
> >
> > Changelog:
> > 06.03.2010 First release
> > 26.03.2010 Fix mutex[1] issue and tested it for compile failure
> >
> > Signed-off-by: Stefani Seibold <stefani(a)seibold.net>
> > ---
> > drivers/mtd/chips/cfi_cmdset_0001.c | 131 +++++++++++++++++-----------------
> > drivers/mtd/chips/cfi_cmdset_0002.c | 122 ++++++++++++++++----------------
> > drivers/mtd/chips/cfi_cmdset_0020.c | 136 +++++++++++++++++-----------------
> > drivers/mtd/chips/fwh_lock.h | 6 +-
> > drivers/mtd/chips/gen_probe.c | 3 +-
> > drivers/mtd/lpddr/lpddr_cmds.c | 79 ++++++++++----------
> > include/linux/mtd/flashchip.h | 4 +-
> > 7 files changed, 239 insertions(+), 242 deletions(-)
>


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From: Andrew Morton on 23 Apr 2010 02:10
On Fri, 23 Apr 2010 08:03:04 +0200 Stefani Seibold <stefani(a)seibold.net> wrote:

> David did not respond to my request since more than a month. Can u apply
> the patch to linux next?

The patch is rather too fundamental for there to be benefit in me
carrying it.

Hopefully Artem can look at it soon, although he's somewhat busy with
real-life things at present.

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From: Artem Bityutskiy on 28 Apr 2010 10:10
On Thu, 2010-04-22 at 23:07 -0400, Andrew Morton wrote:
> On Fri, 23 Apr 2010 08:03:04 +0200 Stefani Seibold <stefani(a)seibold.net> wrote:
>
> > David did not respond to my request since more than a month. Can u apply
> > the patch to linux next?
>
> The patch is rather too fundamental for there to be benefit in me
> carrying it.
>
> Hopefully Artem can look at it soon, although he's somewhat busy with
> real-life things at present.

Yeah, the patch is in my l2 tree, and David should take it to
mtd-2.6.git at some point, so it will probably be in 2.6.35, unless
David misses the merge window :-)

--
Best Regards,
Artem Bityutskiy (Артём Битюцкий)

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