> -----Original Message----- > From: Saurabh Singh Sengar <ssengar@xxxxxxxxxxxxx> > Sent: 23 August 2024 15:00 > To: Saurabh Sengar <ssengar@xxxxxxxxxxxxxxxxxxx>; akpm@linux- > foundation.org; linux-mm@xxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx > Cc: wei.liu@xxxxxxxxxx; srivatsa@xxxxxxxxxxxxx; clameter@xxxxxxx; > mgorman@xxxxxxxxxxxxxxxxxxx > Subject: [EXTERNAL] RE: [PATCH v2] mm/vmstat: Defer the > refresh_zone_stat_thresholds after all CPUs bringup > > > > > -----Original Message----- > > From: Saurabh Sengar <ssengar@xxxxxxxxxxxxxxxxxxx> > > Sent: 12 August 2024 11:44 > > To: akpm@xxxxxxxxxxxxxxxxxxxx; linux-mm@xxxxxxxxx; linux- > > kernel@xxxxxxxxxxxxxxx > > Cc: Saurabh Singh Sengar <ssengar@xxxxxxxxxxxxx>; wei.liu@xxxxxxxxxx; > > srivatsa@xxxxxxxxxxxxx > > Subject: [PATCH v2] mm/vmstat: Defer the refresh_zone_stat_thresholds > > after all CPUs bringup > > > > refresh_zone_stat_thresholds function has two loops which is expensive > > for higher number of CPUs and NUMA nodes. > > > > Below is the rough estimation of total iterations done by these loops > > based on number of NUMA and CPUs. > > > > Total number of iterations: nCPU * 2 * Numa * mCPU > > Where: > > nCPU = total number of CPUs > > Numa = total number of NUMA nodes > > mCPU = mean value of total CPUs (e.g., 512 for 1024 total CPUs) > > > > For the system under test with 16 NUMA nodes and 1024 CPUs, this > > results in a substantial increase in the number of loop iterations > > during boot-up when NUMA is enabled: > > > > No NUMA = 1024*2*1*512 = 1,048,576 : Here > refresh_zone_stat_thresholds > > takes around 224 ms total for all the CPUs in the system under test. > > 16 NUMA = 1024*2*16*512 = 16,777,216 : Here > > refresh_zone_stat_thresholds takes around 4.5 seconds total for all > > the CPUs in the system under test. > > > > Calling this for each CPU is expensive when there are large number of > > CPUs along with multiple NUMAs. Fix this by deferring > > refresh_zone_stat_thresholds to be called later at once when all the > > secondary CPUs are up. Also, register the DYN hooks to keep the > > existing hotplug functionality intact. > > > > Signed-off-by: Saurabh Sengar <ssengar@xxxxxxxxxxxxxxxxxxx> > > CC: Mel Gorman and Christoph Lameter Adding cl@xxxxxxxxx instead of clameter@xxxxxxx for Christoph Lameter - Saurabh
