On Mon, Sep 08, 2014 at 10:46:16AM -0300, Arnaldo Carvalho de Melo wrote: > Em Sat, Sep 06, 2014 at 10:39:15PM +0200, Jiri Olsa escreveu: > > On Fri, Sep 05, 2014 at 11:07:56AM -0300, Arnaldo Carvalho de Melo wrote: > > > Em Fri, Sep 05, 2014 at 11:42:59AM +0300, Adrian Hunter escreveu: > > > > On 09/04/2014 06:19 PM, Arnaldo Carvalho de Melo wrote: > > > > > Em Thu, Sep 04, 2014 at 03:32:08PM +0300, Adrian Hunter escreveu: > > > > No I was meaning something different. For example, 'perf record' opens > > > > an > > > > event for 2 processes per-cpu and gets 4 file descriptors: > > > > > task1 task2 > > > > cpu0 fd0 fd1 > > > > cpu1 fd2 fd3 > > > > > Now, perf record will mmap fd0 and fd2 and set-output fd1->fd0 > > > > and fd3->fd2. > > > > > pollfds includes only fd0 and fd2. > > > > > But if task2 exits, the POLLHUP will appear on fd1 and fd3. > > > > So? We are not interested in fd1 and fd3, since all our reading is done > > > on fd0 and fd2 mmaps, no? > > > hm, what if task1 (fd0, fd2) exits first.. perf record will exit, > > but it still has to read task2..? > > Ok, what happens in that case, i.e. when the fds that were set to be the > ones to be polled, gets nuked, does the set-output command gets just > undone? Or does the mmap stands, receiving the events from the remaining > fds and the polling notifications get sent to, in this case, fd3 and > fd1?
mmaps stays for fd1 and fd3.. and they get poll notifications as well, we just do not check/poll them now > > I'll look at the kernel code for that... > > > > I.e. when we ask the kernel to point fd B to fd A's mmap (what you > > > called set-output) and fd B inserts an event into fd A's mmap ring > > > buffer, we get fd A poll return as POLLRD, no? > > > > Have to check... Otherwise we would have to poll all fds all the time, > > > not just the ones mmaping, right? > > > > > I think Jiri's patchset changed pollfds to include all fds for that > > > > reason. > > > hm, I did not think of that.. ;-) I needed more grained feedback > > for future features like cpu hotplug > > So this is good for something you didn't tried to fix (and document) but > good for something that may be nice in the future? Grumpf, we have > already way too much stuff that will be eventually used but is not used > right now :-\ > IMO it's more clear to poll pm all event FDs.. and now with the case Adrian described it seems necessary anyway jirka -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
