Messages in this thread | | | Date | Tue, 20 Sep 2022 10:36:27 +0800 | Subject | Re: [PATCH v6 2/2] ipc/msg: mitigate the lock contention with percpu counter | From | "Sun, Jiebin" <> |
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On 9/18/2022 8:53 PM, Manfred Spraul wrote: > Hi Jiebin, > > On 9/13/22 21:25, Jiebin Sun wrote: >> The msg_bytes and msg_hdrs atomic counters are frequently >> updated when IPC msg queue is in heavy use, causing heavy >> cache bounce and overhead. Change them to percpu_counter >> greatly improve the performance. Since there is one percpu >> struct per namespace, additional memory cost is minimal. >> Reading of the count done in msgctl call, which is infrequent. >> So the need to sum up the counts in each CPU is infrequent. >> >> Apply the patch and test the pts/stress-ng-1.4.0 >> -- system v message passing (160 threads). >> >> Score gain: 3.99x >> >> CPU: ICX 8380 x 2 sockets >> Core number: 40 x 2 physical cores >> Benchmark: pts/stress-ng-1.4.0 >> -- system v message passing (160 threads) >> >> Signed-off-by: Jiebin Sun <jiebin.sun@intel.com> >> Reviewed-by: Tim Chen <tim.c.chen@linux.intel.com> > Reviewed-by: Manfred Spraul <manfred@colorfullif.com> >> @@ -495,17 +496,18 @@ static int msgctl_info(struct ipc_namespace >> *ns, int msqid, >> msginfo->msgssz = MSGSSZ; >> msginfo->msgseg = MSGSEG; >> down_read(&msg_ids(ns).rwsem); >> - if (cmd == MSG_INFO) { >> + if (cmd == MSG_INFO) >> msginfo->msgpool = msg_ids(ns).in_use; >> - msginfo->msgmap = atomic_read(&ns->msg_hdrs); >> - msginfo->msgtql = atomic_read(&ns->msg_bytes); >> + max_idx = ipc_get_maxidx(&msg_ids(ns)); >> + up_read(&msg_ids(ns).rwsem); >> + if (cmd == MSG_INFO) { >> + msginfo->msgmap = percpu_counter_sum(&ns->percpu_msg_hdrs); >> + msginfo->msgtql = percpu_counter_sum(&ns->percpu_msg_bytes); > > Not caused by your change, it just now becomes obvious: > > msginfo->msgmap and ->msgtql are type int, i.e. signed 32-bit, and the > actual counters are 64-bit. > This can overflow - and I think the code should handle this. Just > clamp the values to INT_MAX. > Hi Manfred,
Thanks for your advice. But I'm not sure if we could fix the overflow issue in ipc/msg totally by
clamp(val, low, INT_MAX). If the value is over s32, we might avoid the reversal sign, but still could
not get the accurate value.
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