FYI, wanted to get this on our radar... seems latest DM isn't allowing RFC readahead code to set a sane readahead default for DM devices? get_capacity() is returning 0 for DM devices (not just multipath). Vivek did share that fdisk -l does show the proper capacity for the DM device. I haven't had a chance to look at the relevant code yet. I've asked Vivek to cc dm-devel on any further messages he might send in response to this thread. ---------- Forwarded message ---------- From: Vivek Goyal <vgoyal@xxxxxxxxxx> Date: Wed, Feb 3, 2010 at 10:58 AM Subject: Re: [PATCH 00/11] [RFC] 512K readahead size with thrashing safe readahead To: Wu Fengguang <fengguang.wu@xxxxxxxxx> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>, Jens Axboe <jens.axboe@xxxxxxxxxx>, Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>, Linux Memory Management List <linux-mm@xxxxxxxxx>, "linux-fsdevel@xxxxxxxxxxxxxxx" <linux-fsdevel@xxxxxxxxxxxxxxx>, LKML <linux-kernel@xxxxxxxxxxxxxxx> On Wed, Feb 03, 2010 at 10:24:54AM -0500, Vivek Goyal wrote: > On Wed, Feb 03, 2010 at 02:27:56PM +0800, Wu Fengguang wrote: > > Vivek, > > > > On Wed, Feb 03, 2010 at 06:38:03AM +0800, Vivek Goyal wrote: > > > On Tue, Feb 02, 2010 at 11:28:35PM +0800, Wu Fengguang wrote: > > > > Andrew, > > > > > > > > This is to lift default readahead size to 512KB, which I believe yields > > > > more I/O throughput without noticeably increasing I/O latency for today's HDD. > > > > > > > > > > Hi Fengguang, > > > > > > I was doing a quick test with the patches. I was using fio to run some > > > sequential reader threads. I have got one access to one Lun from an HP > > > EVA. In my case it looks like with the patches throughput has come down. > > > > Thank you for the quick testing! > > > > This patchset does 3 things: > > > > 1) 512K readahead size > > 2) new readahead algorithms > > 3) new readahead tracing/stats interfaces > > > > (1) will impact performance, while (2) _might_ impact performance in > > case of bugs. > > > > Would you kindly retest the patchset with readahead size manually set > > to 128KB? That would help identify the root cause of the performance > > drop: > > > > DEV=sda > > echo 128 > /sys/block/$DEV/queue/read_ahead_kb > > > > I have got two paths to the HP EVA and got multipath device setup(dm-3). I > noticed with vanilla kernel read_ahead_kb=128 after boot but with your patches > applied it is set to 4. So looks like something went wrong with device > size/capacity detection hence wrong defaults. Manually setting > read_ahead_kb=512, got me better performance as compare to vanilla kernel. > I put a printk in add_disk and noticed that for multipath device get_capacity() is returning 0 and that's why ra_pages is being set to 1. Thanks Vivek -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a> -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
