Re: [PATCH 2/2] drm/amdgpu: fix fence calculation

["Christian König" <ckoenig.leichtzumerken@gmail.com>]

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In this case amdgpu_ctx_fence_time should probably be changed to 
initialize the variable itself.

That is really bad coding style otherwise.

Christian.

Am 11.05.21 um 20:14 schrieb Nieto, David M:
>
> [AMD Official Use Only - Internal Distribution Only]
>
>
> The local variables need to be initialized to zero, since 
> amdgpu_ctx_fence_time accumulates and does not initialize
>
> David
> ------------------------------------------------------------------------
> *From:* Christian König <ckoenig.leichtzumerken@gmail.com>
> *Sent:* Tuesday, May 11, 2021 12:53 AM
> *To:* Nieto, David M <David.Nieto@amd.com>; 
> amd-gfx@lists.freedesktop.org <amd-gfx@lists.freedesktop.org>
> *Subject:* Re: [PATCH 2/2] drm/amdgpu: fix fence calculation
> Am 10.05.21 um 22:29 schrieb David M Nieto:
> > The proper metric for fence utilization over several
> > contexts is an harmonic mean, but such calculation is
> > prohibitive in kernel space, so the code approximates it.
> >
> > Because the approximation diverges when one context has a
> > very small ratio compared with the other context, this change
> > filter out ratios smaller that 0.01%
> >
> > Signed-off-by: David M Nieto <david.nieto@amd.com>
> > Change-Id: I5b6e0ce5f489a5f55855d35354a6a3653e9d613b
> > ---
> >   drivers/gpu/drm/amd/amdgpu/amdgpu_ctx.c | 13 ++++++++++++-
> >   drivers/gpu/drm/amd/amdgpu/amdgpu_ctx.h |  1 +
> >   2 files changed, 13 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ctx.c 
> b/drivers/gpu/drm/amd/amdgpu/amdgpu_ctx.c
> > index 9036c93b4a0c..89ee464b9424 100644
> > --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ctx.c
> > +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ctx.c
> > @@ -698,16 +698,27 @@ ktime_t amdgpu_ctx_mgr_fence_usage(struct 
> amdgpu_ctx_mgr *mgr, uint32_t hwip,
> >        struct amdgpu_ctx_entity *centity;
> >        ktime_t total = 0, max = 0;
> >
> > +
>
> Unrelated white space change.
>
> >        if (idx >= AMDGPU_MAX_ENTITY_NUM)
> >                return 0;
> >        idp = &mgr->ctx_handles;
> >        mutex_lock(&mgr->lock);
> >        idr_for_each_entry(idp, ctx, id) {
> > +             ktime_t ttotal = tmax = ktime_set(0, 0);
>
> There should be a blank line between decleration and code and please
> don't initialize local variables if it isn't necessary.
>
> Christian.
>
> >                if (!ctx->entities[hwip][idx])
> >                        continue;
> >
> >                centity = ctx->entities[hwip][idx];
> > -             amdgpu_ctx_fence_time(ctx, centity, &total, &max);
> > +             amdgpu_ctx_fence_time(ctx, centity, &ttotal, &tmax);
> > +
> > +             /* Harmonic mean approximation diverges for very small
> > +              * values. If ratio < 0.01% ignore
> > +              */
> > +             if (AMDGPU_CTX_FENCE_USAGE_MIN_RATIO(tmax, ttotal))
> > +                     continue;
> > +
> > +             total = ktime_add(total, ttotal);
> > +             max = ktime_after(tmax, max) ? tmax : max;
> >        }
> >
> >        mutex_unlock(&mgr->lock);
> > diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ctx.h 
> b/drivers/gpu/drm/amd/amdgpu/amdgpu_ctx.h
> > index 10dcf59a5c6b..3541dfb059ec 100644
> > --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ctx.h
> > +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ctx.h
> > @@ -30,6 +30,7 @@ struct drm_file;
> >   struct amdgpu_fpriv;
> >
> >   #define AMDGPU_MAX_ENTITY_NUM 4
> > +#define AMDGPU_CTX_FENCE_USAGE_MIN_RATIO(max, total) (max > 
> 16384ULL*total)
> >
> >   struct amdgpu_ctx_entity {
> >        uint64_t                sequence;
>


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