On Fri, Oct 07 2005, Chen, Kenneth W wrote:
> Jens Axboe wrote on Friday, October 07, 2005 12:42 AM
> > > It starts out with scsi_end_request being a fairly hot function in
> the
> > > execution profile, then I noticed blk_queue_start/end_tag() are
> being
> > > called but no actual consumer of using the tag. I'm trying to find
> a
> > > way to avoid making these blk_queue_start/end_tag calls. I got the
> > > answer
> > > now. The proper way is to fix it in the scsi LLDD. Scratch this
> patch,
> > > new patch to follow :-)
> >
> > Ok that makes more sense! But it's a little worrying that
> > blk_queue_end_tag() would show up as hot in the profile, it is
> actually
> > quite lean.
>
> It's probably a very small number that I'm chasing with avoiding blk
> layer tagging. Nevertheless, any number no matter how small, is a gold
> mine to me :-)
>
> Latest execution profile taken with 2.6.14-rc2 kernel with "industry
> standard transaction processing database workload". First column is
> clock ticks (a direct measure of time), 2nd column is instruction
> retired,
> and 3rd column is number of L3 misses occurred inside the function.
>
> Symbol Clockticks Inst. Retired L3 Misses
> scsi_request_fn 8.12% 9.27% 11.18%
> Schedule 6.52% 4.93% 7.26%
> scsi_end_request 4.44% 3.59% 6.76%
> __blockdev_direct_IO 4.28% 4.38% 3.98%
> __make_request 3.59% 4.16% 3.47%
> __wake_up 2.46% 1.56% 3.33%
> dio_bio_end_io 2.14% 1.67% 3.18%
> aio_complete 2.05% 1.27% 3.56%
> kmem_cache_free 1.95% 1.70% 0.71%
> kmem_cache_alloc 1.45% 1.84% 0.45%
> put_page 1.42% 0.60% 1.27%
> follow_hugetlb_page 1.41% 0.75% 1.27%
> __generic_file_aio_read 1.37% 0.36% 1.68%
The above looks pretty much as expected. What change in profile did you
see when eliminating the blk_queue_end_tag() call?
--
Jens Axboe
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