Hi Andi, On Tue, Oct 27, 2020 at 12:21 AM Andi Kleen <a...@linux.intel.com> wrote: > > On Mon, Oct 26, 2020 at 11:19:37PM +0900, Namhyung Kim wrote: > > This patch just added a warning before running it. I'd really want to > > fix the kernel if possible but don't have a good idea. Thoughts? > > The easiest fix would be some multi threading in perf stat opening, then then > extra latencies could be mostly hidden. One thread per group would probably > be overkill, but just a few threads would lower the penalty significantly.
Thanks for the suggestion. Yeah we could use threads to circumvent the problem in userspace. But I think it'd better to solve it in the kernel. Another problem I see is when there's a concurrent perf event in the same context. Since it holds ctx->mutex during the synchronize_rcu the other event should wait for it too. It'd be nice if it can release the ctx->mutex before going to sleep unless we can remove it. > > I think that would be better than this patch and it's likely not that much > more complicated, as this is already a lot of code. > > > +{ > > + const char *known_sw_pmu[] = { > > + "software", "tracepoint", "breakpoint", "kprobe", "uprobe", > > "msr" > > That's a non scalable approach. New pmus get added regularly. It would be > better to > indicate this in a generic way from the kernel. Maybe we can add a new attribute (task_ctx?) for that. > > > + pr_warning("WARNING: Event group has mixed hw/sw > > events.\n" > > + "This will slow down the perf_event_open > > syscall.\n" > > + "Consider putting a hw event as a > > leader.\n\n"); > > You really need to tell the user which group, otherwise it is hard to find > in a large command line. OK Thanks Namhyung