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Date: Mon, 15 Mar 2010 07:15:54 +0100 From: Stefani Seibold <stefani@...bold.net> To: Jamie Lokier <jamie@...reable.org> Cc: Andrew Morton <akpm@...ux-foundation.org>, David Woodhouse <dwmw2@...radead.org>, "Kreuzer, Michael (NSN - DE/Ulm)" <michael.kreuzer@....com>, linux-mtd@...ts.infradead.org, linux-kernel <linux-kernel@...r.kernel.org> Subject: Re: [Patch] fix MTD CFI/LPDDR flash driver huge latency bug Am Montag, den 15.03.2010, 03:03 +0000 schrieb Jamie Lokier: > Stefani Seibold wrote: > > Am Freitag, den 12.03.2010, 23:38 +0000 schrieb Jamie Lokier: > > > Andrew Morton wrote: > > > > On Sat, 06 Mar 2010 17:48:57 +0100 > > > > Stefani Seibold <stefani@...bold.net> wrote: > > > > > > > > > > > > > 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. > > > > > > It would be even better if it also split the critical sections into > > > smaller ones with cond_resched() between, so that non-preemptible > > > kernels benefit too. > > > > The problem is the memcpy operation which is very slow. A cond_resched > > wouldn't help, since the cpu bus is blocked during the transfer of the > > word. > > I mean split the memcpy into multiple smaller memcpys, so that the > total time in each memcpy is limited to something reasonable. > > The check in cond_resched() is fast, especially once cached. memcpy > speed depends a lot on the attached flash and how everything's > configured, varying from 2.5MB/s up to hundreds of MB/s. So how about > doing cond_resched() every 256 bytes? > > -- Jamie I thoght about this aporoach and i don't like this idea. Why not using a preemptible kernel? Stefani -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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