From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:38744) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bII6P-0007xS-II for qemu-devel@nongnu.org; Wed, 29 Jun 2016 12:12:38 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1bII6J-00016P-5X for qemu-devel@nongnu.org; Wed, 29 Jun 2016 12:12:36 -0400 References: <1466598927-5990-1-git-send-email-den@openvz.org> <0bb6c31a-0fb4-175c-fa90-3827e666f6b5@redhat.com> From: "Denis V. Lunev" Message-ID: <5773F355.7050907@openvz.org> Date: Wed, 29 Jun 2016 19:12:05 +0300 MIME-Version: 1.0 In-Reply-To: <0bb6c31a-0fb4-175c-fa90-3827e666f6b5@redhat.com> Content-Type: text/plain; charset="iso-8859-15"; format=flowed Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH 1/1] mirror: fix request throttling in drive-mirror List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Max Reitz , qemu-block@nongnu.org, qemu-devel@nongnu.org Cc: Jeff Cody , Kevin Wolf On 06/29/2016 07:08 PM, Max Reitz wrote: > On 22.06.2016 14:35, Denis V. Lunev wrote: >> There are 2 deficiencies here: >> - mirror_iteration could start several requests inside. Thus we could >> simply have more in_flight requests than MAX_IN_FLIGHT. >> - keeping this in mind throttling in mirror_run which is checking >> s->in_flight == MAX_IN_FLIGHT is wrong. >> >> The patch adds the check and throttling into mirror_iteration and fixes >> the check in mirror_run() to be sure. >> >> Signed-off-by: Denis V. Lunev >> CC: Jeff Cody >> CC: Kevin Wolf >> CC: Max Reitz >> --- >> block/mirror.c | 7 ++++++- >> 1 file changed, 6 insertions(+), 1 deletion(-) >> >> diff --git a/block/mirror.c b/block/mirror.c >> index a04ed9c..e881ef6 100644 >> --- a/block/mirror.c >> +++ b/block/mirror.c >> @@ -399,6 +399,11 @@ static uint64_t coroutine_fn mirror_iteration(MirrorBlockJob *s) >> } >> } >> >> + while (s->in_flight >= MAX_IN_FLIGHT) { >> + trace_mirror_yield_in_flight(s, sector_num, s->in_flight); >> + mirror_wait_for_io(s); >> + } >> + >> mirror_clip_sectors(s, sector_num, &io_sectors); >> switch (mirror_method) { >> case MIRROR_METHOD_COPY: >> @@ -634,7 +639,7 @@ static void coroutine_fn mirror_run(void *opaque) >> */ >> if (qemu_clock_get_ns(QEMU_CLOCK_REALTIME) - last_pause_ns < SLICE_TIME && >> s->common.iostatus == BLOCK_DEVICE_IO_STATUS_OK) { >> - if (s->in_flight == MAX_IN_FLIGHT || s->buf_free_count == 0 || >> + if (s->in_flight >= MAX_IN_FLIGHT || s->buf_free_count == 0 || >> (cnt == 0 && s->in_flight > 0)) { >> trace_mirror_yield(s, s->in_flight, s->buf_free_count, cnt); >> mirror_wait_for_io(s); >> > Using >= seems fine to me, but with the first hunk applied I can't > imagine how s->in_flight should grow beyond MAX_IN_FLIGHT. Don't get me > wrong, I myself like to use >= even where the > case should never > happen, I'm just wondering if I'm missing something here. > > Reviewed-by: Max Reitz > I think that this should not happen anymore, but I'd like to stay on the safe side. Den