On Wed, Jun 10, 2015 at 10:33:32AM +0200, Ingo Molnar wrote: > > * Mel Gorman <mgorman@xxxxxxx> wrote: > > > Linear mapped reader on a 4-node machine with 64G RAM and 48 CPUs > > > > 4.1.0-rc6 4.1.0-rc6 > > vanilla flushfull-v6 > > Ops lru-file-mmap-read-elapsed 162.88 ( 0.00%) 120.81 ( 25.83%) > > > > 4.1.0-rc6 4.1.0-rc6 > > vanillaflushfull-v6r5 > > User 568.96 614.68 > > System 6085.61 4226.61 > > Elapsed 164.24 122.17 > > > > This is showing that the readers completed 25.83% faster with 30% less > > system CPU time. From vmstats, it is known that the vanilla kernel was > > interrupted roughly 900K times per second during the steady phase of the > > test and the patched kernel was interrupts 180K times per second. > > > > The impact is lower on a single socket machine. > > > > 4.1.0-rc6 4.1.0-rc6 > > vanilla flushfull-v6 > > Ops lru-file-mmap-read-elapsed 25.43 ( 0.00%) 20.59 ( 19.03%) > > > > 4.1.0-rc6 4.1.0-rc6 > > vanilla flushfull-v6 > > User 59.14 58.99 > > System 109.15 77.84 > > Elapsed 27.32 22.31 > > > > It's still a noticeable improvement with vmstat showing interrupts went > > from roughly 500K per second to 45K per second. > > Btw., I tried to compare your previous (v5) pfn-tracking numbers with these > full-flushing numbers, and found that the IRQ rate appears to be the same: > That's expected because the number of IPIs sent is the same. What changes is the tracking of the PFNs and then the work within the IPI itself. > > > From vmstats, it is known that the vanilla kernel was interrupted roughly 900K > > > times per second during the steady phase of the test and the patched kernel > > > was interrupts 180K times per second. > > > > It's still a noticeable improvement with vmstat showing interrupts went from > > > roughly 500K per second to 45K per second. > > ... is that because the batching limit in the pfn-tracking case was high enough to > not be noticeable in the vmstat? > It's just the case that there are fewer cores and less activity in the machine overall. > In the full-flushing case (v6 without patch 4) the batching limit is 'infinite', > we'll batch as long as possible, right? > No because we must flush before pages are freed so the maximum batching is related to SWAP_CLUSTER_MAX. If we free a page before the flush then in theory the page can be reallocated and a stale TLB entry can allow access to unrelated data. It would be almost impossible to trigger corruption this way but it's a concern. -- Mel Gorman SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>