On 17.03.22 10:48, CGEL wrote: > On Thu, Mar 17, 2022 at 09:17:13AM +0100, David Hildenbrand wrote: >> On 17.03.22 03:03, CGEL wrote: >>> On Wed, Mar 16, 2022 at 03:56:23PM +0100, David Hildenbrand wrote: >>>> On 16.03.22 14:34, cgel.zte@xxxxxxxxx wrote: >>>>> From: Yang Yang <yang.yang29@xxxxxxxxxx> >>>>> >>>>> Delay accounting does not track the delay of ksm cow. When tasks >>>>> have many ksm pages, it may spend a amount of time waiting for ksm >>>>> cow. >>>>> >>>>> To get the impact of tasks in ksm cow, measure the delay when ksm >>>>> cow happens. This could help users to decide whether to user ksm >>>>> or not. >>>>> >>>>> Also update tools/accounting/getdelays.c: >>>>> >>>>> / # ./getdelays -dl -p 231 >>>>> print delayacct stats ON >>>>> listen forever >>>>> PID 231 >>>>> >>>>> CPU count real total virtual total delay total delay average >>>>> 6247 1859000000 2154070021 1674255063 0.268ms >>>>> IO count delay total delay average >>>>> 0 0 0ms >>>>> SWAP count delay total delay average >>>>> 0 0 0ms >>>>> RECLAIM count delay total delay average >>>>> 0 0 0ms >>>>> THRASHING count delay total delay average >>>>> 0 0 0ms >>>>> KSM count delay total delay average >>>>> 3635 271567604 0ms >>>>> >>>> >>>> TBH I'm not sure how particularly helpful this is and if we want this. >>>> >>> Thanks for replying. >>> >>> Users may use ksm by calling madvise(, , MADV_MERGEABLE) when they want >>> save memory, it's a tradeoff by suffering delay on ksm cow. Users can >>> get to know how much memory ksm saved by reading >>> /sys/kernel/mm/ksm/pages_sharing, but they don't know what the costs of >>> ksm cow delay, and this is important of some delay sensitive tasks. If >>> users know both saved memory and ksm cow delay, they could better use >>> madvise(, , MADV_MERGEABLE). >> >> But that happens after the effects, no? >> >> IOW a user already called madvise(, , MADV_MERGEABLE) and then gets the >> results. >> > Image user are developing or porting their applications on experiment > machine, they could takes those benchmark as feedback to adjust whether > to use madvise(, , MADV_MERGEABLE) or it's range. And why can't they run it with and without and observe performance using existing metrics (or even application-specific metrics?)? -- Thanks, David / dhildenb
