Re: [PATCH] Fix a huge latency problem in the MTD CFI and LPDDRflash drivers.

From: Artem Bityutskiy
Date: Fri Apr 23 2010 - 08:07:21 EST


On Sun, 2010-04-18 at 22:46 +0200, Stefani Seibold wrote:
> From: Stefani Seibold <stefani@xxxxxxxxxxx>
>
> 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@xxxxxxxxxxx>
> ---
> 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 (ÐÑÑÑÐ ÐÐÑÑÑÐÐÐ)

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