On Wed, May 27, 2009 at 10:47:47AM +0800, Hisashi Hifumi wrote: > > At 11:36 09/05/27, Wu Fengguang wrote: > >On Wed, May 27, 2009 at 10:21:53AM +0800, Hisashi Hifumi wrote: > >> > >> At 11:09 09/05/27, Wu Fengguang wrote: > >> >On Wed, May 27, 2009 at 08:25:04AM +0800, Hisashi Hifumi wrote: > >> >> > >> >> At 08:42 09/05/27, Andrew Morton wrote: > >> >> >On Fri, 22 May 2009 10:33:23 +0800 > >> >> >Wu Fengguang <fengguang.wu@xxxxxxxxx> wrote: > >> >> > > >> >> >> > I tested above patch, and I got same performance number. > >> >> >> > I wonder why if (PageUptodate(page)) check is there... > >> >> >> > >> >> >> Thanks! This is an interesting micro timing behavior that > >> >> >> demands some research work. The above check is to confirm if it's > >> >> >> the PageUptodate() case that makes the difference. So why that case > >> >> >> happens so frequently so as to impact the performance? Will it also > >> >> >> happen in NFS? > >> >> >> > >> >> >> The problem is readahead IO pipeline is not running smoothly, which is > >> >> >> undesirable and not well understood for now. > >> >> > > >> >> >The patch causes a remarkably large performance increase. A 9% > >> >> >reduction in time for a linear read? I'd be surprised if the workload > >> >> > >> >> Hi Andrew. > >> >> Yes, I tested this with dd. > >> >> > >> >> >even consumed 9% of a CPU, so where on earth has the kernel gone to? > >> >> > > >> >> >Have you been able to reproduce this in your testing? > >> >> > >> >> Yes, this test on my environment is reproducible. > >> > > >> >Hisashi, does your environment have some special configurations? > >> > >> Hi. > >> My testing environment is as follows: > >> Hardware: HP DL580 > >> CPU:Xeon 3.2GHz *4 HT enabled > >> Memory:8GB > >> Storage: Dothill SANNet2 FC (7Disks RAID-0 Array) > > > >This is a big hardware RAID. What's the readahead size? > > > >The numbers look too small for a 7 disk RAID: > > > > > #dd if=testdir/testfile of=/dev/null bs=16384 > > > > > > -2.6.30-rc6 > > > 1048576+0 records in > > > 1048576+0 records out > > > 17179869184 bytes (17 GB) copied, 224.182 seconds, 76.6 MB/s > > > > > > -2.6.30-rc6-patched > > > 1048576+0 records in > > > 1048576+0 records out > > > 17179869184 bytes (17 GB) copied, 206.465 seconds, 83.2 MB/s > > > >I'd suggest you to configure the array properly before coming back to > >measuring the impact of this patch. > > > I created 16GB file to this disk array, and mounted to testdir, dd to this directory. I mean, you should get >300MB/s throughput with 7 disks, and you should seek ways to achieve that before testing out this patch :-) Thanks, Fengguang -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
