Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> writes: > Quoting Francisco Jerez (2018-07-28 06:20:12) >> Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> writes: >> >> > A recent trend for cpufreq is to boost the CPU frequencies for >> > iowaiters, in particularly to benefit high frequency I/O. We do the same >> > and boost the GPU clocks to try and minimise time spent waiting for the >> > GPU. However, as the igfx and CPU share the same TDP, boosting the CPU >> > frequency will result in the GPU being throttled and its frequency being >> > reduced. Thus declaring iowait negatively impacts on GPU throughput. >> > >> > Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=107410 >> > References: 52ccc4314293 ("cpufreq: intel_pstate: HWP boost performance on IO wakeup") >> >> This patch causes up to ~13% performance regressions (with significance >> 5%) on several latency-sensitive tests on my BXT: >> >> jxrendermark/rendering-test=Linear Gradient Blend/rendering-size=128x128: XXX ±35.69% x53 -> XXX ±32.57% x61 d=-13.52% ±31.88% p=2.58% > The jxrendermark Linear Gradient Blend test-case had probably the smallest effect size of all the regressions I noticed... Can you take a look at any of the other ones instead? > Curious, as this is just a bunch of composites and as with the others, > should never be latency sensitive (at least under bare X11). They are largely latency-sensitive due to the poor pipelining they seem to achieve between their GPU rendering work and the X11 thread. > Fwiw, I double checked this result: > > Broxton J3455, jxrend -num $(for i in $(seq 1 100); do echo 12 128; done) > x noio-1.txt > + io-1.txt > +------------------------------------------------------------------------+ > | + | > | + | > | * | > | +*x | > | + +***+ | > | + +***++ | > | + ****+* + | > | ++x****** x+ x | > | xx **x*******+x* xx* | > | + + xx*xx+***********x**x***x x+ | > |x x+** x**x****************x***x***+ x + x x ++ +| > | |_______MA_______| | > | |________MA__________| | > +------------------------------------------------------------------------+ > N Min Max Median Avg Stddev > x 100 16109.095 16211.579 16152.497 16154.87 19.270749 > + 100 16116.47 16274.973 16152.365 16156.954 25.304398 > No difference proven at 95.0% confidence > > Your variance is much, much higher, are you still using the original > jxrendermark that doesn't wait for rendering completion? I bet, but the other regressing benchmarks shouldn't be affected. > -Chris
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