On 04/06/2016 06:54 PM, Tejun Heo wrote:
Hello,
On Wed, Apr 06, 2016 at 05:51:45PM -0400, Waiman Long wrote:
+ /*
+ * If a statistics count is in the middle of being updated, it
+ * is possible that the above clearing may not work. So we need
+ * to double check again to make sure that the counters are really
+ * cleared. Still there is a still a very small chance that the
+ * second clearing does not work.
+ */
+ for_each_possible_cpu(cpu) {
+ unsigned long *pstats = per_cpu_ptr(pcs->stats, cpu);
+ int stat;
+
+ for (stat = 0; stat< pcs->nstats; stat++, pstats++)
+ if (*pstats)
+ *pstats = 0;
+ }
I don't think this is acceptable.
I am not sure what you mean here by not acceptable. Please enlighten me on
that.
Hmmm... I thought that was pretty clear. Try-twice-and-we-are-probably-okay
is simply not acceptable. Please make it watertight.
Thanks.
OK, I got it now.
We can certainly make it watertight. However, that will certainly
require adding performance overhead in the percpu stats update fast path
which I am not willing to pay.
The purpose of this stat counters reset functionality is to allow
developers to reset the stat counters, run certain workload and see how
things are going in the kernel when the workload completes assuming that
those stat counters are exposed via sysfs, debugfs, etc. The developers
can certainly check the stat counters after the reset to make sure that
they are properly reset. So I don't think we need an airtight way of
doing it. If you have scenarios in your mind that require airtight reset
of the stat counters, please let me know and I will see what I can do
about it.
Cheers,
Longman
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