linux-kernel - Re: RFC: How to adjust the trace pid?

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Date:   Wed, 12 Aug 2020 15:49:23 +0200
From:   Daniel Vetter <daniel.vetter@...ll.ch>
To:     Christian König <ckoenig.leichtzumerken@...il.com>
Cc:     amd-gfx list <amd-gfx@...ts.freedesktop.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Dave Airlie <airlied@...il.com>, Shashank.Sharma@....com,
        Alex Deucher <alexander.deucher@....com>
Subject: Re: RFC: How to adjust the trace pid?

On Wed, Aug 12, 2020 at 3:42 PM Christian König
<ckoenig.leichtzumerken@...il.com> wrote:
>
> Ping? Daniel, Dave any opinion on this?

Type patch, cc: tracing people, see what they say? tbh I have no idea,
but they have been making unhappy noises about some of the tricks
we've played in the past in i915 tracepoints. So not everything is
cool in there.

Otherwise I guess just add another tracepoint parameter to dump the
correct userspace mm.

3rd option could be to dump the current mm (since I'm assuming those
threads do kthread_use/unuse_mm to impersonate the right userspace
process correctly) in the tracepoint infrastructure too?

Cheers, Daniel

> Christian.
>
> Am 07.08.20 um 15:36 schrieb Christian König:
> > Hi everybody,
> >
> > in amdgpu we got the following issue which I'm seeking advise how to cleanly handle it.
> >
> > We have a bunch of trace points which are related to the VM subsystem and executed in either a work item, kthread or foreign process context.
> >
> > Now tracing the pid of the context which we are executing in is not really that useful, so I'm wondering if we could just overwrite the pid recorded in the trace entry?
> >
> > The following patch does exactly that for the vm_grab_id() trace point, but I'm not 100% sure if that is legal or not.
> >
> > Any ideas? Comments?
> >
> > Thanks,
> > Christian.
> >
> >
>


-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch