Andi Kleen <a...@linux.intel.com> writes: > On Tue, Aug 11, 2020 at 12:47:24PM +0300, Alexander Shishkin wrote: >> >> Right, but which bytes? One byte per event? That's >> arbitrary. sizeof(struct perf_event)? Then, probably also sizeof(struct >> perf_event_context). > > Yes the sum of all the sizeofs needed for a perf_event.
Well, *all* of them will be tedious to collect, seeing as there is ctx->task_ctx_data, there is ring_buffer, scheduling trees, there is stuff that pmus allocate under the hood, like AUX SG tables. >> The above two structs add up to 2288 bytes on my local build. Given the >> default RLIMIT_MEMLOCK of 64k, that's 28 events. As opposed to ~1k >> events if we keep using the RLIMIT_NOFILE. Unless I'm missing your >> point. > > Yes that's true. We would probably need to increase the limit to a few > MB at least. Ok, but if we have to increase a limit anyway, we might as well increase the NOFILE. > Or maybe use some combination with the old rlimit for compatibility. > The old rlimit would give an implicit extra RLIMIT_NFILE * 2288 limit > for RLIMIT_MEMLOCK. This would only give full compatibility for a single > perf process, but I suspect that's good enough for most users. We'd need to settle on charging a fixed set of structures per event, then. And, without increasing the file limit, this would still total at 1052 events. We could also involve perf_event_mlock_kb *and* increase it too, but I suspect distros don't just leave it at kernel's default either. Regards, -- Alex
