On 01/30/2019 05:00 PM, Thomas Gleixner wrote: > On Wed, 30 Jan 2019, Andrew Morton wrote: >> On Wed, 30 Jan 2019 13:31:30 +0100 Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote: >> >>> Waiman reported that on large systems with a large amount of interrupts the >>> readout of /proc/stat takes a long time to sum up the interrupt >>> statistics. In principle this is not a problem. but for unknown reasons >>> some enterprise quality software reads /proc/stat with a high frequency. >>> >>> The reason for this is that interrupt statistics are accounted per cpu. So >>> the /proc/stat logic has to sum up the interrupt stats for each interrupt. >>> >>> The following series addresses this by making the interrupt statitics code >>> in the core generate the sum directly and by making the loop in the >>> /proc/stat read function smarter. >>> >> Has the speedup been quantified? > Waiman should be able to provide numbers > > On a 4-socket IvyBridge-EX system (60-core 120-thread) and 3016 irqs, I ran a test program that read /proc/stat 50,000 time. Before the patch, the elapsed time was 18.436s (sys 18.380s). After the patch, it was 3.769s (sys 3.742s). It was an almost 80% reduction in execution time. It was better than I expected. I like that. Cheers, Longman
