linux-kernel - Re: [patch V2 21/29] tracing: Use percpu stack trace buffer more intelligently

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Message-ID: <20190418114629.023b63d7@gandalf.local.home>
Date:   Thu, 18 Apr 2019 11:46:29 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>, x86@...nel.org,
        Andy Lutomirski <luto@...nel.org>,
        Alexander Potapenko <glider@...gle.com>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Pekka Enberg <penberg@...nel.org>, linux-mm@...ck.org,
        David Rientjes <rientjes@...gle.com>,
        Christoph Lameter <cl@...ux.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        kasan-dev@...glegroups.com,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        Akinobu Mita <akinobu.mita@...il.com>,
        iommu@...ts.linux-foundation.org,
        Robin Murphy <robin.murphy@....com>,
        Christoph Hellwig <hch@....de>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Johannes Thumshirn <jthumshirn@...e.de>,
        David Sterba <dsterba@...e.com>, Chris Mason <clm@...com>,
        Josef Bacik <josef@...icpanda.com>,
        linux-btrfs@...r.kernel.org, dm-devel@...hat.com,
        Mike Snitzer <snitzer@...hat.com>,
        Alasdair Kergon <agk@...hat.com>,
        intel-gfx@...ts.freedesktop.org,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        dri-devel@...ts.freedesktop.org, David Airlie <airlied@...ux.ie>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        linux-arch@...r.kernel.org
Subject: Re: [patch V2 21/29] tracing: Use percpu stack trace buffer more
 intelligently

On Thu, 18 Apr 2019 17:43:59 +0200 (CEST)
Thomas Gleixner <tglx@...utronix.de> wrote:

> On Thu, 18 Apr 2019, Steven Rostedt wrote:
> > On Thu, 18 Apr 2019 10:41:40 +0200
> > Thomas Gleixner <tglx@...utronix.de> wrote:  
> > > -static DEFINE_PER_CPU(struct ftrace_stack, ftrace_stack);
> > > +/* This allows 8 level nesting which is plenty */  
> > 
> > Can we make this 4 level nesting and increase the size? (I can see us
> > going more than 64 deep, kernel developers never cease to amaze me ;-)
> > That's all we need:
> > 
> >  Context: Normal, softirq, irq, NMI
> > 
> > Is there any other way to nest?  
> 
> Not that I know, but you are the tracer dude :)
>

There's other places I only test 4 deep, so it should be fine to limit
it to 4 then.

Thanks!

-- Steve