Messages in this thread | | | Date | Tue, 26 May 2009 16:42:52 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH] readahead:add blk_run_backing_dev |
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On Fri, 22 May 2009 10:33:23 +0800 Wu Fengguang <fengguang.wu@intel.com> 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 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?
Thanks.
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