From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.nokia.com ([192.100.122.233] helo=mgw-mx06.nokia.com) by bombadil.infradead.org with esmtps (Exim 4.69 #1 (Red Hat Linux)) id 1O5Her-0002Ig-Cm for linux-mtd@lists.infradead.org; Fri, 23 Apr 2010 12:06:58 +0000 Subject: Re: [PATCH] Fix a huge latency problem in the MTD CFI and LPDDR flash drivers. From: Artem Bityutskiy To: Stefani Seibold In-Reply-To: <1271623604.7050.0.camel@wall-e.seibold.net> References: <1271623604.7050.0.camel@wall-e.seibold.net> Content-Type: text/plain; charset="UTF-8" Date: Fri, 23 Apr 2010 15:03:24 +0300 Message-ID: <1272024204.6917.9.camel@localhost> Mime-Version: 1.0 Content-Transfer-Encoding: 8bit Cc: nico@fluxnic.net, michael.kreuzer@nsn.com, linux-kernel@vger.kernel.org, linux-mtd@lists.infradead.org, akpm@linux-foundation.org, dwmw2@infradead.org Reply-To: dedekind1@gmail.com List-Id: Linux MTD discussion mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Sun, 2010-04-18 at 22:46 +0200, Stefani Seibold wrote: > From: Stefani Seibold > > 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 > --- > 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)