From ef2198aad1cba51dff27ca5c9680c6c9a5fc608b Mon Sep 17 00:00:00 2001 From: mikeb Date: Fri, 5 Aug 2016 18:16:04 +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. From FreeBSD. --- sys/dev/pv/hyperv.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) diff --git a/sys/dev/pv/hyperv.c b/sys/dev/pv/hyperv.c index 1aba89795e1..7a8e22cca19 100644 --- a/sys/dev/pv/hyperv.c +++ b/sys/dev/pv/hyperv.c @@ -534,7 +534,7 @@ hv_event_intr(struct hv_softc *sc) int cpu = CPU_INFO_UNIT(ci); int bit, dword, maxdword, relid; struct hv_channel *ch; - uint32_t *revents; + uint32_t *revents, pending; evt = (struct hv_synic_event_flags *)sc->sc_siep[cpu] + HV_MESSAGE_SINT; if ((sc->sc_proto == HV_VMBUS_VERSION_WS2008) || @@ -559,8 +559,9 @@ hv_event_intr(struct hv_softc *sc) for (dword = 0; dword < maxdword; dword++) { if (revents[dword] == 0) continue; - for (bit = 0; bit < 32; bit++) { - if (!atomic_clearbit_ptr(&revents[dword], bit)) + pending = atomic_swap_uint(&revents[dword], 0); + for (bit = 0; pending > 0; pending >>= 1, bit++) { + if ((pending & 1) == 0) continue; relid = (dword << 5) + bit; /* vmbus channel protocol message */ -- 2.20.1