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

[Nirmoy Das <nirmoy.das@linux.intel.com>]

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.


>   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.


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@intel.com>
>> Suggested-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
>> Signed-off-by: Nirmoy Das <nirmoy.das@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
>>