* xen-blkback: Scheduled work from previous purge is still busy, cannot purge list
@ 2020-10-13 5:26 J. Roeleveld
2020-10-15 10:57 ` Roger Pau Monné
0 siblings, 1 reply; 5+ messages in thread
From: J. Roeleveld @ 2020-10-13 5:26 UTC (permalink / raw)
To: xen-devel
Hi All,
I am seeing the following message in the "dmesg" output of a driver domain.
[Thu Oct 8 20:57:04 2020] xen-blkback: Scheduled work from previous purge is
still busy, cannot purge list
[Thu Oct 8 20:57:11 2020] xen-blkback: Scheduled work from previous purge is
still busy, cannot purge list
[Thu Oct 8 20:57:44 2020] xen-blkback: Scheduled work from previous purge is
still busy, cannot purge list
[Thu Oct 8 20:57:44 2020] xen-blkback: Scheduled work from previous purge is
still busy, cannot purge list
Is this something to worry about? Or can I safely ignore this?
--
Joost
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: xen-blkback: Scheduled work from previous purge is still busy, cannot purge list
2020-10-13 5:26 xen-blkback: Scheduled work from previous purge is still busy, cannot purge list J. Roeleveld
@ 2020-10-15 10:57 ` Roger Pau Monné
[not found] ` <1855015.FeAb16qnYt@eve>
0 siblings, 1 reply; 5+ messages in thread
From: Roger Pau Monné @ 2020-10-15 10:57 UTC (permalink / raw)
To: J. Roeleveld; +Cc: xen-devel
On Tue, Oct 13, 2020 at 07:26:47AM +0200, J. Roeleveld wrote:
> Hi All,
>
> I am seeing the following message in the "dmesg" output of a driver domain.
>
> [Thu Oct 8 20:57:04 2020] xen-blkback: Scheduled work from previous purge is
> still busy, cannot purge list
> [Thu Oct 8 20:57:11 2020] xen-blkback: Scheduled work from previous purge is
> still busy, cannot purge list
> [Thu Oct 8 20:57:44 2020] xen-blkback: Scheduled work from previous purge is
> still busy, cannot purge list
> [Thu Oct 8 20:57:44 2020] xen-blkback: Scheduled work from previous purge is
> still busy, cannot purge list
>
>
> Is this something to worry about? Or can I safely ignore this?
What version of the Linux kernel are you running in that driver
domain?
Is the domain very busy? That might explain the delay in purging
grants.
Also is this an sporadic message, or it's constantly repeating?
Roger.
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: xen-blkback: Scheduled work from previous purge is still busy, cannot purge list
[not found] ` <1855015.FeAb16qnYt@eve>
@ 2020-10-15 12:00 ` Roger Pau Monné
2020-10-15 12:53 ` J. Roeleveld
0 siblings, 1 reply; 5+ messages in thread
From: Roger Pau Monné @ 2020-10-15 12:00 UTC (permalink / raw)
To: J. Roeleveld; +Cc: xen-devel
Please don't drop xen-devel mailing list when replying.
On Thu, Oct 15, 2020 at 01:28:49PM +0200, J. Roeleveld wrote:
> On Thursday, October 15, 2020 12:57:35 PM CEST you wrote:
> > On Tue, Oct 13, 2020 at 07:26:47AM +0200, J. Roeleveld wrote:
> > > Hi All,
> > >
> > > I am seeing the following message in the "dmesg" output of a driver
> > > domain.
> > >
> > > [Thu Oct 8 20:57:04 2020] xen-blkback: Scheduled work from previous purge
> > > is still busy, cannot purge list
> > > [Thu Oct 8 20:57:11 2020] xen-blkback: Scheduled work from previous purge
> > > is still busy, cannot purge list
> > > [Thu Oct 8 20:57:44 2020] xen-blkback: Scheduled work from previous purge
> > > is still busy, cannot purge list
> > > [Thu Oct 8 20:57:44 2020] xen-blkback: Scheduled work from previous purge
> > > is still busy, cannot purge list
> > >
> > >
> > > Is this something to worry about? Or can I safely ignore this?
> >
> > What version of the Linux kernel are you running in that driver
> > domain?
>
> Host:
> Kernel: 5.4.66
> Xen: 4.12.3
>
> Driver domain:
> Kernel: 5.4.66
> Xen: 4.12.3
>
>
> > Is the domain very busy? That might explain the delay in purging
> > grants.
>
> No, it's generally asleep, been going through the munin-records and can't find
> any spikes the correlate with the messages either.
>
> > Also is this an sporadic message, or it's constantly repeating?
>
> It's sporadic, but occasionally, I get it several times in a row.
>
> My understanding of the code where this message comes from is far from
> sufficient. Which means I have no clue what it is actually trying to do.
There's a recurrent worker thread in blkback that will go and purge
unused cache entries after they have expired. This is done to prevent
the cache from growing unbounded.
AFAICT this just means the worker is likely running faster than what
you can proceed, and hence you get another worker run before the old
entries have been removed. Should be safe to ignore, but makes me
wonder if I should add a parameter to tune the periodicity of the
purge work.
Roger.
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: xen-blkback: Scheduled work from previous purge is still busy, cannot purge list
2020-10-15 12:00 ` Roger Pau Monné
@ 2020-10-15 12:53 ` J. Roeleveld
2020-10-15 13:05 ` Roger Pau Monné
0 siblings, 1 reply; 5+ messages in thread
From: J. Roeleveld @ 2020-10-15 12:53 UTC (permalink / raw)
To: xen-devel
On Thursday, October 15, 2020 2:00:46 PM CEST Roger Pau Monné wrote:
> Please don't drop xen-devel mailing list when replying.
My apologies, most mailing lists I am active on have a working "reply" button.
Here I need to use "reply-all".
> On Thu, Oct 15, 2020 at 01:28:49PM +0200, J. Roeleveld wrote:
> > On Thursday, October 15, 2020 12:57:35 PM CEST you wrote:
> > > On Tue, Oct 13, 2020 at 07:26:47AM +0200, J. Roeleveld wrote:
> > > > Hi All,
> > > >
> > > > I am seeing the following message in the "dmesg" output of a driver
> > > > domain.
> > > >
> > > > [Thu Oct 8 20:57:04 2020] xen-blkback: Scheduled work from previous
> > > > purge
> > > > is still busy, cannot purge list
> > > > [Thu Oct 8 20:57:11 2020] xen-blkback: Scheduled work from previous
> > > > purge
> > > > is still busy, cannot purge list
> > > > [Thu Oct 8 20:57:44 2020] xen-blkback: Scheduled work from previous
> > > > purge
> > > > is still busy, cannot purge list
> > > > [Thu Oct 8 20:57:44 2020] xen-blkback: Scheduled work from previous
> > > > purge
> > > > is still busy, cannot purge list
> > > >
> > > >
> > > > Is this something to worry about? Or can I safely ignore this?
> > >
> > > What version of the Linux kernel are you running in that driver
> > > domain?
> >
> > Host:
> > Kernel: 5.4.66
> > Xen: 4.12.3
> >
> > Driver domain:
> > Kernel: 5.4.66
> > Xen: 4.12.3
> >
> > > Is the domain very busy? That might explain the delay in purging
> > > grants.
> >
> > No, it's generally asleep, been going through the munin-records and can't
> > find any spikes the correlate with the messages either.
> >
> > > Also is this an sporadic message, or it's constantly repeating?
> >
> > It's sporadic, but occasionally, I get it several times in a row.
> >
> > My understanding of the code where this message comes from is far from
> > sufficient. Which means I have no clue what it is actually trying to do.
>
> There's a recurrent worker thread in blkback that will go and purge
> unused cache entries after they have expired. This is done to prevent
> the cache from growing unbounded.
>
> AFAICT this just means the worker is likely running faster than what
> you can proceed, and hence you get another worker run before the old
> entries have been removed. Should be safe to ignore, but makes me
> wonder if I should add a parameter to tune the periodicity of the
> purge work.
In other words, when it "fails" in this manner, the queue will simply be left
and processed the next time?
How often does this currently run?
A parameter to tune the periodicity might be an option, for now I feel
confident I can safely ignore these messages.
Thanks,
Joost
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: xen-blkback: Scheduled work from previous purge is still busy, cannot purge list
2020-10-15 12:53 ` J. Roeleveld
@ 2020-10-15 13:05 ` Roger Pau Monné
0 siblings, 0 replies; 5+ messages in thread
From: Roger Pau Monné @ 2020-10-15 13:05 UTC (permalink / raw)
To: J. Roeleveld; +Cc: xen-devel
On Thu, Oct 15, 2020 at 02:53:34PM +0200, J. Roeleveld wrote:
> On Thursday, October 15, 2020 2:00:46 PM CEST Roger Pau Monné wrote:
> > Please don't drop xen-devel mailing list when replying.
>
> My apologies, most mailing lists I am active on have a working "reply" button.
> Here I need to use "reply-all".
>
>
> > On Thu, Oct 15, 2020 at 01:28:49PM +0200, J. Roeleveld wrote:
> > > On Thursday, October 15, 2020 12:57:35 PM CEST you wrote:
> > > > On Tue, Oct 13, 2020 at 07:26:47AM +0200, J. Roeleveld wrote:
> > > > > Hi All,
> > > > >
> > > > > I am seeing the following message in the "dmesg" output of a driver
> > > > > domain.
> > > > >
> > > > > [Thu Oct 8 20:57:04 2020] xen-blkback: Scheduled work from previous
> > > > > purge
> > > > > is still busy, cannot purge list
> > > > > [Thu Oct 8 20:57:11 2020] xen-blkback: Scheduled work from previous
> > > > > purge
> > > > > is still busy, cannot purge list
> > > > > [Thu Oct 8 20:57:44 2020] xen-blkback: Scheduled work from previous
> > > > > purge
> > > > > is still busy, cannot purge list
> > > > > [Thu Oct 8 20:57:44 2020] xen-blkback: Scheduled work from previous
> > > > > purge
> > > > > is still busy, cannot purge list
> > > > >
> > > > >
> > > > > Is this something to worry about? Or can I safely ignore this?
> > > >
> > > > What version of the Linux kernel are you running in that driver
> > > > domain?
> > >
> > > Host:
> > > Kernel: 5.4.66
> > > Xen: 4.12.3
> > >
> > > Driver domain:
> > > Kernel: 5.4.66
> > > Xen: 4.12.3
> > >
> > > > Is the domain very busy? That might explain the delay in purging
> > > > grants.
> > >
> > > No, it's generally asleep, been going through the munin-records and can't
> > > find any spikes the correlate with the messages either.
> > >
> > > > Also is this an sporadic message, or it's constantly repeating?
> > >
> > > It's sporadic, but occasionally, I get it several times in a row.
> > >
> > > My understanding of the code where this message comes from is far from
> > > sufficient. Which means I have no clue what it is actually trying to do.
> >
> > There's a recurrent worker thread in blkback that will go and purge
> > unused cache entries after they have expired. This is done to prevent
> > the cache from growing unbounded.
> >
> > AFAICT this just means the worker is likely running faster than what
> > you can proceed, and hence you get another worker run before the old
> > entries have been removed. Should be safe to ignore, but makes me
> > wonder if I should add a parameter to tune the periodicity of the
> > purge work.
>
> In other words, when it "fails" in this manner, the queue will simply be left
> and processed the next time?
Yes, exactly.
> How often does this currently run?
The purge worked will run every 100ms, and the queued work should be
terminated before the next run.
> A parameter to tune the periodicity might be an option, for now I feel
> confident I can safely ignore these messages.
Sure, I'm testing a patch series to that effect now.
Thanks, Roger.
^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2020-10-15 13:05 UTC | newest]
Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed)
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2020-10-13 5:26 xen-blkback: Scheduled work from previous purge is still busy, cannot purge list J. Roeleveld
2020-10-15 10:57 ` Roger Pau Monné
[not found] ` <1855015.FeAb16qnYt@eve>
2020-10-15 12:00 ` Roger Pau Monné
2020-10-15 12:53 ` J. Roeleveld
2020-10-15 13:05 ` Roger Pau Monné
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