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Message-ID: <20120131144734.GA4378@redhat.com> Date: Tue, 31 Jan 2012 09:47:34 -0500 From: Vivek Goyal <vgoyal@...hat.com> To: Shaohua Li <shaohua.li@...el.com> Cc: lkml <linux-kernel@...r.kernel.org>, linux-mm <linux-mm@...ck.org>, Andrew Morton <akpm@...ux-foundation.org>, Jens Axboe <axboe@...nel.dk>, Herbert Poetzl <herbert@...hfloor.at>, Eric Dumazet <eric.dumazet@...il.com>, Wu Fengguang <wfg@...ux.intel.com> Subject: Re: [PATCH] fix readahead pipeline break caused by block plug On Tue, Jan 31, 2012 at 03:59:40PM +0800, Shaohua Li wrote: > Herbert Poetzl reported a performance regression since 2.6.39. The test > is a simple dd read, but with big block size. The reason is: > > T1: ra (A, A+128k), (A+128k, A+256k) > T2: lock_page for page A, submit the 256k > T3: hit page A+128K, ra (A+256k, A+384). the range isn't submitted > because of plug and there isn't any lock_page till we hit page A+256k > because all pages from A to A+256k is in memory > T4: hit page A+256k, ra (A+384, A+ 512). Because of plug, the range isn't > submitted again. Why IO is not submitted because of plug? Doesn't task now get scheduled out causing an unplug? IOW, are we now busy waiting somewhere preventing unplug? Thanks Vivek -- 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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