softirq: reduce latencies

Date	Thu, 03 Jan 2013 23:49:40 -0800

In various network workloads, __do_softirq() latencies can be up
to 20 ms if HZ=1000, and 200 ms if HZ=100.

This is because we iterate 10 times in the softirq dispatcher,
and some actions can consume a lot of cycles.

This patch changes the fallback to ksoftirqd condition to :

- A time limit of 2 ms.
- need_resched() being set on current task

When one of this condition is met, we wakeup ksoftirqd for further
softirq processing if we still have pending softirqs.

Using need_resched() as the only condition can trigger RCU stalls,
as we can keep BH disabled for too long.

I ran several benchmarks and got no significant difference in
throughput, but a very significant reduction of latencies (one order
of magnitude) :

In following bench, 200 antagonist "netperf -t TCP_RR" are started in
background, using all available cpus.

Then we start one "netperf -t TCP_RR", bound to the cpu handling the NIC
IRQ (hard+soft)

Before patch :

RT_LATENCY,MIN_LATENCY,MAX_LATENCY,P50_LATENCY,P90_LATENCY,P99_LATENCY,MEAN_LATENCY,STDDEV_LATENCY
MIGRATED TCP REQUEST/RESPONSE TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET
to 7.7.7.84 () port 0 AF_INET : first burst 0 : cpu bind
RT_LATENCY=550110.424
MIN_LATENCY=146858
MAX_LATENCY=997109
P50_LATENCY=305000
P90_LATENCY=550000
P99_LATENCY=710000
MEAN_LATENCY=376989.12
STDDEV_LATENCY=184046.92
After patch :

RT_LATENCY,MIN_LATENCY,MAX_LATENCY,P50_LATENCY,P90_LATENCY,P99_LATENCY,MEAN_LATENCY,STDDEV_LATENCY
MIGRATED TCP REQUEST/RESPONSE TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET
to 7.7.7.84 () port 0 AF_INET : first burst 0 : cpu bind
RT_LATENCY=40545.492
MIN_LATENCY=9834
MAX_LATENCY=78366
P50_LATENCY=33583
P90_LATENCY=59000
P99_LATENCY=69000
MEAN_LATENCY=38364.67
STDDEV_LATENCY=12865.26

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: David Miller <davem@davemloft.net>
Cc: Tom Herbert <therbert@google.com>
Cc: Ben Hutchings <bhutchings@solarflare.com>

Signed-off-by: Paul Reioux <reioux@gmail.com>
writeback: fix race that cause writeback hung
msm: kgsl: Add intermediate power levels

Make use of the two independent power domains to
add intermediate levels.  Attempt to just increase
the bus frequency before also raising the GPU
frequency.

Change-Id: Ie2109df001f96e36e03959288aa957d63c0ef4a7
Signed-off-by: Lucille Sylvester <lsylvest@codeaurora.org>
Signed-off-by: Carter Cooper <ccooper@codeaurora.org>
Signed-off-by: Francisco Franco <franciscofranco.1990@gmail.com>

Conflicts:
	drivers/gpu/msm/kgsl_pwrctrl.c
	drivers/gpu/msm/kgsl_pwrctrl.h
msm: kgsl: set active pwrlevel to init pwrlevel after power collapse

Between kgsl_open and kgsl_release calls active pwrlevel could be
set to anything based on the content. However after a power collapse
always power up the GPU and set the clock to init level.

Change-Id: Ic2858218afa9c1047864ab8551b3495b7d752952
Signed-off-by: Suman Tatiraju <sumant@codeaurora.org>
Signed-off-by: Carter Cooper <ccooper@codeaurora.org>
Signed-off-by: Francisco Franco <franciscofranco.1990@gmail.com>
gpu: Interactive Gov by Franco
acpuclock: losen l2 settings