Re: [PATCH] proc/stat: Separate out individual irq counts into /proc/stat_irqs

[Waiman Long]

On 04/19/2018 01:38 PM, Randy Dunlap wrote:
> On 04/19/18 10:09, Waiman Long wrote:
>> It was found that reading /proc/stat could be time consuming on
>> systems with a lot of irqs. For example, reading /proc/stat in a
>> certain 2-socket Skylake server took about 4.6ms because it had over
>> 5k irqs. In that particular case, the majority of the CPU cycles for
>> reading /proc/stat was spent in the kstat_irqs() function.  Therefore,
>> application performance can be impacted if the application reads
>> /proc/stat rather frequently.
>>
>> The "intr" line within /proc/stat contains a sum total of all the irqs
>> that have happened followed by a list of irq counts for each individual
>> irq number. In many cases, the first number is good enough. The
>> individual irq counts may not provide that much more information.
>>
>> In order to avoid this kind of performance issue, all these individual
>> irq counts are now separated into a new /proc/stat_irqs file. The
>> sum total irq count will stay in /proc/stat and be duplicated in
>> /proc/stat_irqs. Applications that need to look up individual irq counts
>> will now have to look into /proc/stat_irqs instead of /proc/stat.
>>
>> Signed-off-by: Waiman Long <longman@xxxxxxxxxx>
>> ---
>>  fs/proc/stat.c | 48 +++++++++++++++++++++++++++++++++++++++++-------
>>  1 file changed, 41 insertions(+), 7 deletions(-)
> Also please update Documentation/filesystems/proc.txt.
>
> thanks,

Right. I forgot to do that. Will send out v2 to fix that.

-Longman