Hi Namhyung, On Mon, Nov 25, 2024 at 09:42:54PM -0800, Namhyung Kim wrote: > Thanks for the report and the test code. I agree that the current man > page is a little confusing about the overflow notification. I can see > the following sentences in the "overflow handling" section. > > There are two ways to generate overflow notifications. > > The first is to set a wakeup_events or wakeup_watermark value that > will trigger if a certain number of samples or bytes have been > written to the mmap ring buffer. In this case, POLL_IN is indicated. > > The other way is by use of the PERF_EVENT_IOC_REFRESH ioctl. This > ioctl adds to a counter that decrements each time the event > overflows. When nonzero, POLL_IN is indicated, but once the counter > reaches 0 POLL_HUP is indicated and the underlying event is disabled. > > I think the first and the default way uses the ring buffer to determine > overflow condition so it should be allocated before calling poll(2) or > similar. The second way doesn't seem to require ring buffers, but I > haven't tested it actually. > > Maybe we can add something like this to the first section: > > If the ring buffer is not allocated, POLL_HUP is indicated. Thanks! Would you mind sending a patch? Have a lovely day! Alex -- <https://www.alejandro-colomar.es/>
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