linux-kernel - Re: [PATCH 0/2] vhost: improve livepatch switching for heavily loaded vhost worker kthreads

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Message-ID: <20230127044355.frggdswx424kd5dq@treble>
Date:   Thu, 26 Jan 2023 20:43:55 -0800
From:   Josh Poimboeuf <jpoimboe@...nel.org>
To:     "Seth Forshee (DigitalOcean)" <sforshee@...italocean.com>
Cc:     Petr Mladek <pmladek@...e.com>, Jason Wang <jasowang@...hat.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Jiri Kosina <jikos@...nel.org>,
        Miroslav Benes <mbenes@...e.cz>,
        Joe Lawrence <joe.lawrence@...hat.com>,
        virtualization@...ts.linux-foundation.org, kvm@...r.kernel.org,
        netdev@...r.kernel.org, live-patching@...r.kernel.org,
        linux-kernel@...r.kernel.org, Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH 0/2] vhost: improve livepatch switching for heavily
 loaded vhost worker kthreads

On Thu, Jan 26, 2023 at 03:12:35PM -0600, Seth Forshee (DigitalOcean) wrote:
> On Thu, Jan 26, 2023 at 06:03:16PM +0100, Petr Mladek wrote:
> > On Fri 2023-01-20 16:12:20, Seth Forshee (DigitalOcean) wrote:
> > > We've fairly regularaly seen liveptches which cannot transition within kpatch's
> > > timeout period due to busy vhost worker kthreads.
> > 
> > I have missed this detail. Miroslav told me that we have solved
> > something similar some time ago, see
> > https://lore.kernel.org/all/20220507174628.2086373-1-song@kernel.org/
> 
> Interesting thread. I had thought about something along the lines of the
> original patch, but there are some ideas in there that I hadn't
> considered.

Here's another idea, have we considered this?  Have livepatch set
TIF_NEED_RESCHED on all kthreads to force them into schedule(), and then
have the scheduler call klp_try_switch_task() if TIF_PATCH_PENDING is
set.

Not sure how scheduler folks would feel about that ;-)

-- 
Josh