Hi Peter, > On Aug 22, 2019, at 12:47 AM, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote: > > On Wed, Aug 21, 2019 at 06:43:49PM +0000, Yonghong Song wrote: >> On 8/21/19 11:31 AM, Peter Zijlstra wrote: > >>> So extending PERF_RECORD_LOST doesn't work. But PERF_FORMAT_LOST might >>> still work fine; but you get to implement it for all software events. >> >> Could you give more specifics about PERF_FORMAT_LOST? Googling >> "PERF_FORMAT_LOST" only yields two emails which we are discussing here :-( > > Look at what the other PERF_FORMAT_ flags do? Basically it is adding a > field to the read(2) output. Do we need to implement PERF_FORMAT_LOST for all software events? If user space asks for PERF_FORMAT_LOST for events that do not support it, can we just fail sys_perf_event_open()? Thanks, Song
