Quoting Antonio Argenziano (2018-02-13 22:47:35)
> 
> 
> On 13/02/18 01:26, Chris Wilson wrote:
> > icl offers a much reduced context space, and in its simplest setup we
> > cannot allocate one context per priority level, so trim the number and
> > reuse the same context for multiple priority requests.
> > 
> > Signed-off-by: Chris Wilson <ch...@chris-wilson.co.uk>
> > ---
> >   tests/gem_exec_schedule.c | 38 +++++++++++++++++++++++---------------
> >   1 file changed, 23 insertions(+), 15 deletions(-)
> > 
> > diff --git a/tests/gem_exec_schedule.c b/tests/gem_exec_schedule.c
> > index 05f7ae38..ec02d994 100644
> > --- a/tests/gem_exec_schedule.c
> > +++ b/tests/gem_exec_schedule.c
> > @@ -43,6 +43,8 @@
> >   #define BUSY_QLEN 8
> >   #define MAX_ELSP_QLEN 16
> >   
> > +#define MAX_CONTEXTS 256
> > +
> >   IGT_TEST_DESCRIPTION("Check that we can control the order of execution");
> >   
> >   static void store_dword(int fd, uint32_t ctx, unsigned ring,
> > @@ -556,8 +558,8 @@ static void preemptive_hang(int fd, unsigned ring)
> >   static void deep(int fd, unsigned ring)
> >   {
> >   #define XS 8
> > -     const unsigned int nctx = MAX_PRIO - MIN_PRIO;
> > -     const unsigned size = ALIGN(4*nctx, 4096);
> > +     const unsigned int nreq = MAX_PRIO - MIN_PRIO;
> > +     const unsigned size = ALIGN(4*nreq, 4096);
> >       struct timespec tv = {};
> >       struct cork cork;
> >       uint32_t result, dep[XS];
> > @@ -565,10 +567,9 @@ static void deep(int fd, unsigned ring)
> >       uint32_t *ptr;
> >       uint32_t *ctx;
> >   
> > -     ctx = malloc(sizeof(*ctx) * nctx);
> > -     for (int n = 0; n < nctx; n++) {
> > +     ctx = malloc(sizeof(*ctx) * MAX_CONTEXTS);
> > +     for (int n = 0; n < MAX_CONTEXTS; n++) {
> >               ctx[n] = gem_context_create(fd);
> > -             gem_context_set_priority(fd, ctx[n], MAX_PRIO - nctx + n);
> >       }
> >   
> >       result = gem_create(fd, size);
> > @@ -592,7 +593,7 @@ static void deep(int fd, unsigned ring)
> >               execbuf.buffers_ptr = to_user_pointer(obj);
> >               execbuf.buffer_count = XS + 2;
> >               execbuf.flags = ring;
> > -             for (int n = 0; n < nctx; n++) {
> > +             for (int n = 0; n < MAX_CONTEXTS; n++) {
> >                       execbuf.rsvd1 = ctx[n];
> >                       gem_execbuf(fd, &execbuf);
> >               }
> > @@ -603,22 +604,29 @@ static void deep(int fd, unsigned ring)
> >       plug(fd, &cork);
> >   
> >       /* Create a deep dependency chain, with a few branches */
> > -     for (int n = 0; n < nctx && igt_seconds_elapsed(&tv) < 8; n++)
> > +     for (int n = 0; n < nreq && igt_seconds_elapsed(&tv) < 8; n++) {
> > +             uint32_t context = ctx[n % MAX_CONTEXTS];
> 
> Doesn't this introduce some intra-context dependency we didn't have 
> before? Do we care?

Yes, it reduces the re-ordering possibilities (it will also exercise
priority inversion within the context as well). We have to reduce the
test somehow, and this preserves the essence in that the kernel has to
manage the same long dependencies chains, just now with a few more
branches.
-Chris
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