linux-kernel - Re: [PATCH v5 1/8] smp: Run functions concurrently in smp_call_function_many

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Message-ID: <YC5jpNts1QDtXyMH@hirez.programming.kicks-ass.net>
Date:   Thu, 18 Feb 2021 13:55:00 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Nadav Amit <namit@...are.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Rik van Riel <riel@...riel.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>
Subject: Re: [PATCH v5 1/8] smp: Run functions concurrently in
 smp_call_function_many_cond()

On Wed, Feb 17, 2021 at 01:02:41AM +0000, Nadav Amit wrote:
> > On Feb 16, 2021, at 10:59 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> > 
> > On Tue, Feb 16, 2021 at 06:53:09PM +0000, Nadav Amit wrote:
> >>> On Feb 16, 2021, at 8:32 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> > 
> >>> I'm not sure I can explain it yet. It did get me looking at
> >>> on_each_cpu() and it appears that wants to be converted too, something
> >>> like the below perhaps.
> >> 
> >> Looks like a good cleanup, but I cannot say I understand the problem and how
> >> it would solve it. Err...
> > 
> > Yeah, me neither. Bit of a mystery so far.
> 
> This stall seems to be real. Intuitively I presumed preemption was
> mistakenly enabled, but it does not seem so.
> 
> Any chance you can build the kernel with “CONFIG_CSD_LOCK_WAIT_DEBUG=Y” and
> rerun it? Perhaps that output will tell us more.

Sadly not my system. It's a KernelCI box.