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Tvrtko Ursulin authored
By reading the CSB (slow MMIO accesses) into a temporary local buffer we can decrease the duration of holding the execlist lock. Main advantage is that during heavy batch buffer submission we reduce the execlist lock contention, which should decrease the latency and CPU usage between the submitting userspace process and interrupt handling. Downside is that we need to grab and relase the forcewake twice, but as the below numbers will show this is completely hidden by the primary gains. Testing with "gem_latency -n 100" (submit batch buffers with a hundred nops each) shows more than doubling of the throughput and more than halving of the dispatch latency, overall latency and CPU time spend in the submitting process. Submitting empty batches ("gem_latency -n 0") does not seem significantly affected by this change with throughput and CPU time improving by half a percent, and overall latency worsening by the same amount. Above tests were done in a hundred runs on a big core Broadwell. v2: * Overflow protection to local CSB buffer. * Use closer dev_priv in execlists_submit_requests. (Chris Wilson) v3: Rebase. v4: Added commend about irq needed to be disabled in execlists_submit_request. (Chris Wilson) Signed-off-by:
Tvrtko Ursulin <tvrtko.ursulin@intel.com> Cc: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by:
Chris Wilsno <chris@chris-wilson.co.uk> Link: http://patchwork.freedesktop.org/patch/msgid/1458219586-20452-1-git-send-email-tvrtko.ursulin@linux.intel.com
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