Re: [PATCH 2/2] /proc/stat: Add sysctl parameter to control irq counts latency

From: Waiman Long
Date: Mon Jan 07 2019 - 11:19:20 EST

On 01/07/2019 11:14 AM, Matthew Wilcox wrote:
> On Mon, Jan 07, 2019 at 11:07:47AM -0500, Waiman Long wrote:
>>> Why are you caching the _output_ of calling sprintf(), rather than caching the
>>> values of each interrupt?
>> It is just faster to dump the whole string buffer than redoing the
>> number formatting each time when the values don't change. I can cache
>> the individual sums instead if it is the preferred by most.
> But it also consumes more memory. Can you gather some measurements to
> find out what the performance difference is if you cache the values
> instead of the strings?

I allocate 11 bytes (10 digits + space) for each unsigned int IRQ value.
I needs 4 bytes for the unsigned value itself. So it is a saving of 7
bytes. With 4k irqs, it will be 28k.

I will run some measurements of caching the values versus saving the
string later this week.