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Message-ID: <20130130180731.GA9449@gulag1.americas.sgi.com>
Date: Wed, 30 Jan 2013 12:07:32 -0600
From: Nathan Zimmer <nzimmer@....com>
To: cpufreq@...r.kernel.org, linux-pm@...r.kernel.org,
linux-kernel@...r.kernel.org
Cc: "Rafael J. Wysocki" <rjw@...k.pl>
Subject: cpufreq: cpufreq_driver_lock is quite hot on 512p systems
I am noticing the cpufreq_driver_lock is quite hot.
Currently on an idle 512 system perf shows me most of the system time is
spent on this lock.
- 84.18% [kernel] [k] _raw_spin_lock_irqsave
- _raw_spin_lock_irqsave
- 99.97% __cpufreq_cpu_get
cpufreq_cpu_get
__cpufreq_driver_getavg
dbs_check_cpu
od_dbs_timer
process_one_work
worker_thread
kthread
ret_from_fork
The data this lock protects is used in a read mostly situation.
While exprimenting I found turning the lock to a rwlock fixed the problem.
It seems like this might be amenable to using the RCU.
Any other ideas on how to properly resolve the issue?
Thanks,
Nate
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