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

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Message-ID: <20230127170946.zey6xbr4sm4kvh3x@treble>
Date:   Fri, 27 Jan 2023 09:09:46 -0800
From:   Josh Poimboeuf <jpoimboe@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Petr Mladek <pmladek@...e.com>,
        Joe Lawrence <joe.lawrence@...hat.com>, kvm@...r.kernel.org,
        "Michael S. Tsirkin" <mst@...hat.com>, netdev@...r.kernel.org,
        Jiri Kosina <jikos@...nel.org>, linux-kernel@...r.kernel.org,
        virtualization@...ts.linux-foundation.org,
        "Seth Forshee (DigitalOcean)" <sforshee@...italocean.com>,
        live-patching@...r.kernel.org, Miroslav Benes <mbenes@...e.cz>
Subject: Re: [PATCH 0/2] vhost: improve livepatch switching for heavily
 loaded vhost worker kthreads

On Fri, Jan 27, 2023 at 08:52:38AM -0800, Josh Poimboeuf wrote:
> On Fri, Jan 27, 2023 at 11:37:02AM +0100, Peter Zijlstra wrote:
> > On Thu, Jan 26, 2023 at 08:43:55PM -0800, Josh Poimboeuf wrote:
> > > 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 ;-)
> 
> Hmmmm, with preemption I guess the above doesn't work for kthreads
> calling cond_resched() instead of what vhost_worker() does (explicit
> need_resched/schedule).

Though I guess we could hook into cond_resched() too if we make it a
non-NOP for PREEMPT+LIVEPATCH?

-- 
Josh