Messages in this thread | | | Date | Fri, 22 Jun 2018 12:56:13 +0100 | From | Al Viro <> | Subject | Re: [lkp-robot] [fs] 3deb642f0d: will-it-scale.per_process_ops -8.8% regression |
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On Fri, Jun 22, 2018 at 01:53:00PM +0200, Christoph Hellwig wrote:
> > Now, ->sk_wq is modified only in sock_init_data() and sock_graft(); > > the latter, IIRC, is ->accept() helper. Do we ever call either of > > those on a sock of already opened file? IOW, is there any real > > reason for socket ->get_poll_head() not to be constant, other > > than wanting to keep POLL_BUSY_LOOP handling out of ->poll_mask()? > > I agree that POLL_BUSY_LOOP is ugly as hell, but you *still* have > > sock_poll_mask() not free from it... > > I'd have to defer to networking folks if busy looping after pollwait > is what they want, but I suspect the answer is no, by the time > we are already waiting for the queue busy waiting seems pointless.
So mark that in ->f_mode - I strongly suspect that sk_can_busy_loop(sock->sk) can't change while an opened file is there. And lift that (conditional on new FMODE_BUSY_LOOP) into do_poll() and do_select() - we *already* have bits of pieces of that logics in there and that way they'd at least be gathered in one place.
Then replace ->get_poll_head() with file->f_poll_head and see what it gives.
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