On Fri, Oct 07 2005, Andrew Vasquez wrote:
> On Fri, 07 Oct 2005, Chen, Kenneth W wrote:
>
> > 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.
>
> Yes, please let us know what your benchmarking measurements show. I
> take it you are planning on doing something like:
>
> --- a/drivers/scsi/qla2xxx/qla_os.c
> +++ b/drivers/scsi/qla2xxx/qla_os.c
> @@ -1101,10 +1101,7 @@ qla2xxx_slave_configure(struct scsi_devi
> scsi_qla_host_t *ha = to_qla_host(sdev->host);
> struct fc_rport *rport = starget_to_rport(sdev->sdev_target);
>
> - if (sdev->tagged_supported)
> - scsi_activate_tcq(sdev, 32);
> - else
> - scsi_deactivate_tcq(sdev, 32);
> + scsi_adjust_queue_depth(sdev, scsi_get_tag_type(sdev), depth);
>
> rport->dev_loss_tmo = ha->port_down_retry_count + 5;
Ken later posted the patch to linux-scsi, it's very similar to yours.
I doubt the profile will show a significant change, however it is indeed
a little silly to setup the block queueing if it's not going to be used.
Doing the work twice in different code paths is never going to be a win
:-)
--
Jens Axboe
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