[dm-devel] [PATCH] multipathd: "san_path_err" failure optimization

[Martin Wilck]

On Tue, 2019-08-27 at 19:57 +0000, Martin Wilck wrote:
> On Tue, 2019-08-27 at 12:28 +0000, Chongyun Wu wrote:
> > Hi Martin and Ben,
> > 
> > Cloud you help to view below patch, thanks.
> > 
> > From a7126e33e7eff8a985600b41b1723ee66b183586 Mon Sep 17 00:00:00
> > 2001
> > From: Chongyun Wu <wu.chongyun at h3c.com>
> > Date: Tue, 27 Aug 2019 10:23:50 +0800
> > Subject: [PATCH] multipathd: "san_path_err" failure optimization
> > 
> > Let san_path_err_recovery_time path unstable can be
> > detected and not reinstate it until this path keep up in
> > san_path_err_recovery_time. It will fix heavy IO delay
> > caused by parts of paths state shaky in multipath device.
> > 
> > Test and result:
> > Run up eth1 30s and down eth1 30s with 100 loops script to
> > make some paths shaky in each multipath devices.
> > Using below multipath.conf configure in defaults section:
> >     san_path_err_recovery_time 30
> >     san_path_err_threshold 2
> >     san_path_err_forget_rate 6
> > After test, not found any IO delay logs except several logs in the
> > very
> > beginning which before san_path_err filter shaky path works .
> > If without above config and this patch there will be lots of IO
> > delay
> > in syslog and some paths state change from up to down again and
> > again.
> > 
> > Signed-off-by: Chongyun Wu <wu.chongyun at h3c.com>
> > ---
> >  multipathd/main.c | 17 +++++++++++++++++
> >  1 file changed, 17 insertions(+)
> > 
> 
> Hello Chongyun,
> 
> Your patch makes sense to me. Ben has worked much more than myself on
> marginal paths recently, so I'd want to see his opinion, too.

I've now tested this, and indeed it improves the behavior of the
san_path_err algorithm. It's also consistent with how delay_wait_checks
used to behave. So:

Reviewed-by: Martin Wilck <mwilck at suse.com>