[igt-dev] [Intel-gfx] [PATCH i-g-t] benchmarks/gem_wsim: Perturb static_vcs selection across clients

[Tvrtko Ursulin]

On 14/05/2019 11:05, Chris Wilson wrote:
> Use the client id to alternate the static_vcs balancer (-b context)
> across clients - otherwise all clients end up on vcs0 and do not match
> the context balancing employed by media-driver.
> 
> This may want to be behind the -R flag, but I felt it was a fundamental
> property of static context balancing that to keep it disabled by default
> causes unfair comparisons and poor workload scheduling, defeating the
> purpose of testing.

I see your reasoning but it also completely matches the design of other 
balancers to keep it under control of -R switch. It can also already be 
achieved with the -G switch. Which is perhaps a bit confusing.. Having 
both would still make sense I think. (-G gives out engines rr to 
contexts sequentially across all clients, -R start each client contexts 
by rr.)

But I wouldn't enable it unconditionally. Because consider another 
balancer like rr and a two same workload instances of a long context 
followed by short second context batch. If suffers the same problem of 
poor scheduling until -R is added.

So I think we want to have the two balancers compatible in behaviour in 
this respect.
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> ---
>   benchmarks/gem_wsim.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/benchmarks/gem_wsim.c b/benchmarks/gem_wsim.c
> index afb9644dd..8c7e30eb4 100644
> --- a/benchmarks/gem_wsim.c
> +++ b/benchmarks/gem_wsim.c
> @@ -939,7 +939,7 @@ alloc_step_batch(struct workload *wrk, struct w_step *w, unsigned int flags)
>   static void
>   prepare_workload(unsigned int id, struct workload *wrk, unsigned int flags)
>   {
> -	unsigned int ctx_vcs = 0;
> +	unsigned int ctx_vcs = id & 1;

Therefore I think "ctx_vcs = (flags & INITVCSRR) ? id & 1 : 0" here.

>   	int max_ctx = -1;
>   	struct w_step *w;
>   	int i;
> 

Regards,

Tvrtko