Re: high overhead of functions blkg_*stats_* in bfq

Il giorno 06 nov 2017, alle ore 17:13, Jens Axboe [off-list ref] ha =

scritto:

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On 11/06/2017 09:11 AM, Paolo Valente wrote:

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Il giorno 06 nov 2017, alle ore 16:47, Paolo Valente =

[off-list ref] ha scritto:

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Il giorno 06 nov 2017, alle ore 16:00, Tejun Heo [off-list ref] ha =

scritto:

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Hello,
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On Sun, Nov 05, 2017 at 07:21:01PM -0700, Jens Axboe wrote:

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It's pointless to give up on this so soon, when no effort has =

apparently

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been dedicated to figuring out what the actual issue is yet. So =

no, no

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patch that will just disable the stats is going to be accepted.
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That said, I have no idea who uses these stats. Surely someone can
answer that question. Tejun?

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Except for the basic bytes / ios counts, it's all debug fluff, =

which

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should have been hidden behind a debug boot param or go under =

debugfs.

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I'm not sure we can get rid of them at this point for cfq but I =

don't

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see why we'd have them for bfq.
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Ok, then I think this is the right time to ask you what I can throw
way for bfq.  According to your documentation, basic non-debug stats
should be:
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blkio.time
blkio.time_recursive
blkio.sectors
blkio.io_service_bytes
blkio.io_service_bytes_recursive
blkio.io_serviced
blkio.io_serviced_recursive
blkio.io_service_time
blkio.io_service_time_recursive
blkio.io_wait_time
blkio.io_wait_time_recursive
blkio.io_merged
blkio.io_merged_recursive
blkio.io_queued
blkio.io_queued_recursive
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So, I have to keep them in bfq, right?  Or is there something I can
remove for bfq, in your opinion?  Of course, I would be very happy =

to remove stuff!

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Or, more mildly, could some of these stats be moved behind
CONFIG_DEBUG_BLK_CGROUP?

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It'd be nice to have them be runtime enabled, but I don't think
that's a hard requirement at all.

So, you mean *all* stats dynamically enabled/disabled, and disabled by
default.  Plus, some of them also statically filtered, that is
enabled/disabled, through CONFIG_DEBUG_BLK_CGROUP.  Is my
understanding correct?  If it is, we will be happy to do it.

Thanks,
Paolo

So if you can just move them
under DEBUG_BLK_CGROUP, that should be good enough.
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Jens Axboe
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