On Thu, Jul 31, 2014 at 09:48:32AM +0100, Mel Gorman wrote:
> On Thu, Jul 31, 2014 at 01:50:35PM +0800, Aaron Lu wrote:
> > FYI, we noticed the below changes on
> >
> > git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git master
> > commit b72fd1470c9735f53485d089aa918dc327a86077 ("mm: rearrange zone fields
> > into read-only, page alloc, statistics and page reclaim lines")
> >
> > test case: lkp-st02/dd-write/5m-11HDD-JBOD-cfq-xfs-10dd
> >
> > e28c951ff01a805 b72fd1470c9735f53485d089a
> > --------------- -------------------------
> > 1.06 ~ 6% -41.7% 0.62 ~ 3% TOTAL
> > perf-profile.cpu-cycles.get_page_from_freelist.__alloc_pages_nodemask.alloc_pages_current.__page_cache_alloc.pagecache_get_page
> > 1.34 ~ 2% -19.8% 1.07 ~ 2% TOTAL
> > perf-profile.cpu-cycles.__block_write_begin.xfs_vm_write_begin.generic_perform_write.xfs_file_buffered_aio_write.xfs_file_write_iter
> > 1.19 ~ 5% -12.1% 1.05 ~ 4% TOTAL
> > perf-profile.cpu-cycles.copy_from_user_atomic_iovec.iov_iter_copy_from_user_atomic.generic_perform_write.xfs_file_buffered_aio_write.xfs_file_write_iter
> > 2.78 ~ 1% -16.3% 2.32 ~ 4% TOTAL
> > perf-profile.cpu-cycles.__clear_user.read_zero.read_zero.vfs_read.sys_read
> > 2.96e+09 ~ 4% -5.2% 2.806e+09 ~ 0% TOTAL perf-stat.cache-misses
> > 3.86e+12 ~ 5% -5.2% 3.658e+12 ~ 1% TOTAL perf-stat.ref-cycles
> >
> > Legend:
> > ~XX% - stddev percent
> > [+-]XX% - change percent
> >
>
> I'm not exactly sure what I'm reading here. I think it is reporting on cpu
> cycles and cache misses used in various kernel functions. It's not clear what
> the units are but it looks like percentages of overall cycles spent in the
> reported functions. That may or may not be good depending on whether there
> is a higher cost elsewhere pushing the percentages down but that detail
> is not in the report. It looks like this is reporting that fewer clock
> cycles are being spent and incurring fewer cache misses. What is the problem?
LKP does not report problems only, it will also report commits that make
things better :-)
>From the perf-stat.cache-misses, I think it is indicating your commit
does something for good.
Thanks,
Aaron
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