On Thu, 23 Dec 2010 12:30:29 +0000, Chris Wilson <[email protected]> wrote: > On Thu, 23 Dec 2010 12:07:22 +0000, Chris Wilson <[email protected]> > wrote: > > I tweaked the patch to pass the watermark structs through to the check > > routine. The box survives s2ram, but I have now also experienced the > > mysterious slow down after resuming. > > As Eric first said the cause for the slow down is that writing through the > GTT becomes very slow: > > Before suspending: > Time to pwrite 16k through the CPU: 0.000004s > Time to read 16k through a GTT map: 0.000901s > Time to write 16k through a GTT map: 0.000023s > Time to read 16k (again) through a GTT map: 0.000900s > Time to pwrite 16k through the GTT: 0.000007s > > After resume: > Time to pwrite 16k through the CPU: 0.000004s > Time to read 16k through a GTT map: 0.000900s > Time to write 16k through a GTT map: 0.000876s > Time to read 16k (again) through a GTT map: 0.000899s > Time to pwrite 16k through the GTT: 0.000431s > > The implication being that our mapping goes from write-combining to > uncached? > -Chris
I found that the results were not just "slow like no write combining", but timing-dependent, too. Repeated runs of a timing app would get fast sometimes, slow other times, and sometimes the switch from fast->slow or slow->fast would happen in the middle of a run.
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