linux-kernel - Re: [PATCH] Fix a huge latency problem in the MTD CFI and LPDDR flash drivers.

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Message-ID: <1272024204.6917.9.camel@localhost>
Date:	Fri, 23 Apr 2010 15:03:24 +0300
From:	Artem Bityutskiy <dedekind1@...il.com>
To:	Stefani Seibold <stefani@...bold.net>
Cc:	linux-mtd@...ts.infradead.org, linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org, dwmw2@...radead.org,
	michael.kreuzer@....com, nico@...xnic.net
Subject: Re: [PATCH] Fix a huge latency problem in the MTD CFI and LPDDR
 flash drivers.

On Sun, 2010-04-18 at 22:46 +0200, Stefani Seibold wrote:
> From: Stefani Seibold <stefani@...bold.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@...bold.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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