Jens Axboe wrote on Friday, October 07, 2005 1:08 AM
> > 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?
I haven't make any measurement yet. The original patch was an RFC, and
I want to hear opinions from the experts first. I will do a measurement
with the change in qla2x00 driver and I will let you know how much
difference does it make. Most likely, clock ticks in scsi_request_fn
and
scsi_end_request should be reduced. It will be interesting to see L3
misses stats as well.
- Ken
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