From 30494642db82acd378f52a5034c9b671ff98f9f2 Mon Sep 17 00:00:00 2001 From: mikeb Date: Fri, 5 Aug 2016 18:31:21 +0000 Subject: [PATCH] Switch pending event clearing to an atomic swap operation Rather than performing an atomic bit clearing for every encountered event bit set we can adjust the code to perform an atomic swap of a single row of the events array and decrease the amount of expensive atomic operations. Same optimization as for Hyper-V. From FreeBSD. --- sys/dev/pv/xen.c | 11 ++++++----- 1 file changed, 6 insertions(+), 5 deletions(-) diff --git a/sys/dev/pv/xen.c b/sys/dev/pv/xen.c index 2ec7c4c7230..f03d7459300 100644 --- a/sys/dev/pv/xen.c +++ b/sys/dev/pv/xen.c @@ -1,4 +1,4 @@ -/* $OpenBSD: xen.c,v 1.60 2016/08/03 17:14:41 mikeb Exp $ */ +/* $OpenBSD: xen.c,v 1.61 2016/08/05 18:31:21 mikeb Exp $ */ /* * Copyright (c) 2015 Mike Belopuhov @@ -628,13 +628,14 @@ xen_intr(void) for (row = 0; selector > 0; selector >>= 1, row++) { if ((selector & 1) == 0) continue; - pending = sc->sc_ipg->evtchn_pending[row] & - ~(sc->sc_ipg->evtchn_mask[row]); + if ((sc->sc_ipg->evtchn_pending[row] & + ~(sc->sc_ipg->evtchn_mask[row])) == 0) + continue; + pending = atomic_swap_ulong(&sc->sc_ipg->evtchn_pending[row], + 0) & ~(sc->sc_ipg->evtchn_mask[row]); for (bit = 0; pending > 0; pending >>= 1, bit++) { if ((pending & 1) == 0) continue; - atomic_clearbit_ptr(&sc->sc_ipg->evtchn_pending[row], - bit); port = (row * LONG_BIT) + bit; if ((xi = xen_lookup_intsrc(sc, port)) == NULL) { printf("%s: unhandled interrupt on port %u\n", -- 2.20.1