Re: [PATCH v7 1/2] cpufreq: schedutil: Make iowait boost more energy efficient

[Joel Fernandes]

On Mon, Jul 24, 2017 at 1:57 AM, Viresh Kumar <viresh.kumar@xxxxxxxxxx> wrote:
> On 23-07-17, 08:54, Joel Fernandes wrote:
>> Currently the iowait_boost feature in schedutil makes the frequency go to max
>> on iowait wakeups.  This feature was added to handle a case that Peter
>> described where the throughput of operations involving continuous I/O requests
>> [1] is reduced due to running at a lower frequency, however the lower
>> throughput itself causes utilization to be low and hence causing frequency to
>> be low hence its "stuck".
>>
>> Instead of going to max, its also possible to achieve the same effect by
>> ramping up to max if there are repeated in_iowait wakeups happening. This patch
>> is an attempt to do that. We start from a lower frequency (policy->min)
>> and double the boost for every consecutive iowait update until we reach the
>> maximum iowait boost frequency (iowait_boost_max).
>>
>> I ran a synthetic test (continuous O_DIRECT writes in a loop) on an x86 machine
>> with intel_pstate in passive mode using schedutil. In this test the iowait_boost
>> value ramped from 800MHz to 4GHz in 60ms. The patch achieves the desired improved
>> throughput as the existing behavior.
>>
>> [1] https://patchwork.kernel.org/patch/9735885/
>>
>> Cc: Srinivas Pandruvada <srinivas.pandruvada@xxxxxxxxxxxxxxx>
>> Cc: Len Brown <lenb@xxxxxxxxxx>
>> Cc: Rafael J. Wysocki <rjw@xxxxxxxxxxxxx>
>> Cc: Viresh Kumar <viresh.kumar@xxxxxxxxxx>
>> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
>> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
>> Suggested-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
>> Suggested-by: Viresh Kumar <viresh.kumar@xxxxxxxxxx>
>> Signed-off-by: Joel Fernandes <joelaf@xxxxxxxxxx>
>> ---
>>  kernel/sched/cpufreq_schedutil.c | 38 ++++++++++++++++++++++++++++++++------
>>  1 file changed, 32 insertions(+), 6 deletions(-)
>
> You Send V7 [1-2]/2 twice, Are they different ?

No they are the same. Rafael suggested reposting it with linux-pm in
CC I just resent it.

>
> For both the patches:
>
> Acked-by: Viresh Kumar <viresh.kumar@xxxxxxxxxx>

Thanks!

-Joel