From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Fri, 12 Mar 2010 14:23:44 -0800 From: Andrew Morton To: Stefani Seibold Subject: Re: [Patch] fix MTD CFI/LPDDR flash driver huge latency bug Message-Id: <20100312142344.174bd46f.akpm@linux-foundation.org> In-Reply-To: <1267894137.18869.0.camel@wall-e> References: <1267894137.18869.0.camel@wall-e> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Cc: David Woodhouse , "Kreuzer, Michael \(NSN - DE/Ulm\)" , linux-mtd@lists.infradead.org, linux-kernel List-Id: Linux MTD discussion mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Sat, 06 Mar 2010 17:48:57 +0100 Stefani Seibold wrote: > This patch fix a huge latency problem in the MTD CFI and LPDDR flash > drivers. > > 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 change all the use of spin_lock operations for xxxx->mutex > into mutex operations, which is exact what the name says and means. > > There is no performance regression since the mutex is normally not > acquired. hm, big scary patch. Are you sure this mutex is never taken from atomic or irq contexts? Is it ully tested with all relevant debug options and lockdep enabled?