[PATCH] drm/xe/guc: Configure TLB timeout based on CT buffer size

[Matthew Brost]

On Wed, Jun 26, 2024 at 09:33:46AM +0200, Nirmoy Das wrote:
> Hi Matt,
> 
> On 6/26/2024 12:12 AM, Matthew Brost wrote:
> > On Tue, Jun 25, 2024 at 10:49:47AM +0200, Nirmoy Das wrote:
> > > GuC TLB invalidation depends on GuC to process the request from the CT
> > > queue and then the real time to invalidate TLB. Add a function to return
> > > overestimated possible time a TLB inval H2G might take which can be used
> > > as timeout value for TLB invalidation wait time.
> > > 
> > Not reviewing this patch as some reviews seem to be inflight, just
> > adding some thoughts. I will say that this patch looks correct as a
> > short term fix.
> > 
> > Longterm I think we need explore coalescing TLB invalidations targeting
> > the same VM when pressure exists (VM bind case, [1] should help here
> > a bit) or
> 
> I assume you mean to queue tlb requests in kernel for sometime and then
> coalesce before sending.
> 

Yes exactly. A rough idea would be:

- Have a water mark between TLB invalidation seqno of send / recv
- If difference between send / recv is higher than the water mark, start
  holding TLB invalidations in the kernel coalescing them in each VM
- Once we drop below another water mark of send / recv, issue all
  coalesced TLB invalidations

> 
> >   optimize out invalidations
> What do you mean ? Queue ggtt invalidation and send only one ?
> >   (GGTT case, at one point I had
> > logic in for this but pulled it out as it was buggy).
> > 
> > I say this because when debugging [2] I found that lots of TLB
> > invalidations can overwhelm the GuC to the point where it can barely
> > make forward progess on submissions.
> This sounds very serious!
> > The former is likely a fairly large refactor, while the latter shouldn't
> > be too difficult.
> > 
> > Something for us to keep in mind as a group.
> 
> Created https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/2162 to track
> it.
> 

Great! Thanks! Maybe add some of comments from this reply to that?

Matt

> 
> Thanks,
> 
> Nirmoy
> 
> > 
> > Matt
> > 
> > [1] https://patchwork.freedesktop.org/series/133034/
> > [2] https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/799#note_2449497https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/799#note_2449497
> > 
> > > Closes: https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/1622
> > > Cc: Matthew Brost <matthew.brost at intel.com>
> > > Suggested-by: Daniele Ceraolo Spurio <daniele.ceraolospurio at intel.com>
> > > Signed-off-by: Nirmoy Das <nirmoy.das at intel.com>
> > > ---
> > >   drivers/gpu/drm/xe/xe_gt_tlb_invalidation.c |  2 +-
> > >   drivers/gpu/drm/xe/xe_guc_ct.c              | 12 ++++++++++++
> > >   drivers/gpu/drm/xe/xe_guc_ct.h              |  2 ++
> > >   3 files changed, 15 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/drivers/gpu/drm/xe/xe_gt_tlb_invalidation.c b/drivers/gpu/drm/xe/xe_gt_tlb_invalidation.c
> > > index e1f1ccb01143..fa61070d6201 100644
> > > --- a/drivers/gpu/drm/xe/xe_gt_tlb_invalidation.c
> > > +++ b/drivers/gpu/drm/xe/xe_gt_tlb_invalidation.c
> > > @@ -17,7 +17,7 @@
> > >   #include "xe_trace.h"
> > >   #include "regs/xe_guc_regs.h"
> > > -#define TLB_TIMEOUT	(HZ / 4)
> > > +#define TLB_TIMEOUT	xe_guc_tlb_timeout_jiffies()
> > >   static void xe_gt_tlb_fence_timeout(struct work_struct *work)
> > >   {
> > > diff --git a/drivers/gpu/drm/xe/xe_guc_ct.c b/drivers/gpu/drm/xe/xe_guc_ct.c
> > > index b4137fe195a4..e30c0da86acc 100644
> > > --- a/drivers/gpu/drm/xe/xe_guc_ct.c
> > > +++ b/drivers/gpu/drm/xe/xe_guc_ct.c
> > > @@ -112,6 +112,18 @@ ct_to_xe(struct xe_guc_ct *ct)
> > >   #define CTB_G2H_BUFFER_SIZE	(4 * CTB_H2G_BUFFER_SIZE)
> > >   #define G2H_ROOM_BUFFER_SIZE	(CTB_G2H_BUFFER_SIZE / 4)
> > > +/**
> > > + * xe_guc_tlb_timeout_jiffies - Calculate the maximum time to process a tlb inval command
> > > + *
> > > + * This function computes the maximum time to process a tlb inval H2G commands
> > > + * in jiffies. A 4KB buffer full of commands takes a little over a second to process,
> > > + * so this time is set to 2 seconds to be safe.
> > > + */
> > > +long xe_guc_tlb_timeout_jiffies(void)
> > > +{
> > > +	return (CTB_H2G_BUFFER_SIZE * HZ) / SZ_2K;
> > > +}
> > > +
> > >   static size_t guc_ct_size(void)
> > >   {
> > >   	return 2 * CTB_DESC_SIZE + CTB_H2G_BUFFER_SIZE +
> > > diff --git a/drivers/gpu/drm/xe/xe_guc_ct.h b/drivers/gpu/drm/xe/xe_guc_ct.h
> > > index 105bb8e99a8d..a9755574d6c9 100644
> > > --- a/drivers/gpu/drm/xe/xe_guc_ct.h
> > > +++ b/drivers/gpu/drm/xe/xe_guc_ct.h
> > > @@ -64,4 +64,6 @@ xe_guc_ct_send_block_no_fail(struct xe_guc_ct *ct, const u32 *action, u32 len)
> > >   	return xe_guc_ct_send_recv_no_fail(ct, action, len, NULL);
> > >   }
> > > +long xe_guc_tlb_timeout_jiffies(void);
> > > +
> > >   #endif
> > > -- 
> > > 2.42.0
> > >