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rcuperf: Add comments explaining the high reader overhead

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This commit adds comments explaining why the readers have otherwise insane
levels of measurement overhead, namely that they are intended as a test
load for update-side performance measurements, not as a straight-up
read-side performance test.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit is contained in:
Paul E. McKenney 2020-05-25 09:22:24 -07:00
parent 653ed64b01
commit 708cda3165
1 changed files with 9 additions and 2 deletions
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11
kernel/rcu/rcuperf.c
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@ -69,6 +69,11 @@ MODULE_AUTHOR("Paul E. McKenney <paulmck@linux.ibm.com>");
* value specified by nr_cpus for a read-only test.
*
* Various other use cases may of course be specified.
*
* Note that this test's readers are intended only as a test load for
* the writers. The reader performance statistics will be overly
* pessimistic due to the per-critical-section interrupt disabling,
* test-end checks, and the pair of calls through pointers.
*/
#ifdef MODULE
@ -309,8 +314,10 @@ static void rcu_perf_wait_shutdown(void)
}
/*
* RCU perf reader kthread. Repeatedly does empty RCU read-side
* critical section, minimizing update-side interference.
* RCU perf reader kthread. Repeatedly does empty RCU read-side critical
* section, minimizing update-side interference. However, the point of
* this test is not to evaluate reader performance, but instead to serve
* as a test load for update-side performance testing.
*/
static int
rcu_perf_reader(void *arg)