From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:58723) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ai2bt-0003rl-8a for qemu-devel@nongnu.org; Mon, 21 Mar 2016 12:23:18 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ai2bp-0008OT-B8 for qemu-devel@nongnu.org; Mon, 21 Mar 2016 12:23:17 -0400 Received: from mail-wm0-x232.google.com ([2a00:1450:400c:c09::232]:32779) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ai2bp-0008OI-4l for qemu-devel@nongnu.org; Mon, 21 Mar 2016 12:23:13 -0400 Received: by mail-wm0-x232.google.com with SMTP id l68so158329122wml.0 for ; Mon, 21 Mar 2016 09:23:13 -0700 (PDT) From: =?UTF-8?q?Alex=20Benn=C3=A9e?= Date: Mon, 21 Mar 2016 16:23:05 +0000 Message-Id: <1458577386-9984-2-git-send-email-alex.bennee@linaro.org> In-Reply-To: <1458577386-9984-1-git-send-email-alex.bennee@linaro.org> References: <1458577386-9984-1-git-send-email-alex.bennee@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Subject: [Qemu-devel] [PATCH v1 1/2] cpus: don't use atomic_read for vm_clock_warp_start List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Cc: peter.maydell@linaro.org, Peter Crosthwaite , sbruno@freebsd.org, pbonzini@redhat.com, =?UTF-8?q?Alex=20Benn=C3=A9e?= , Richard Henderson As vm_clock_warp_start is a 64 bit value this causes problems for the compiler trying to come up with a suitable atomic operation on 32 bit hosts. The variable documentation says this is meant to be protected by vm_clock_seqlock so lets just move the code into that section. All other references to vm_clock_warp_start are already protected by the seqlock. Signed-off-by: Alex Bennée --- cpus.c | 12 ++++-------- 1 file changed, 4 insertions(+), 8 deletions(-) diff --git a/cpus.c b/cpus.c index 23cf7aa..2fd5381 100644 --- a/cpus.c +++ b/cpus.c @@ -338,15 +338,10 @@ static int64_t qemu_icount_round(int64_t count) static void icount_warp_rt(void) { - /* The icount_warp_timer is rescheduled soon after vm_clock_warp_start - * changes from -1 to another value, so the race here is okay. - */ - if (atomic_read(&vm_clock_warp_start) == -1) { - return; - } + bool check_clock = false; seqlock_write_lock(&timers_state.vm_clock_seqlock); - if (runstate_is_running()) { + if (vm_clock_warp_start != -1 && runstate_is_running()) { int64_t clock = REPLAY_CLOCK(REPLAY_CLOCK_VIRTUAL_RT, cpu_get_clock_locked()); int64_t warp_delta; @@ -362,11 +357,12 @@ static void icount_warp_rt(void) warp_delta = MIN(warp_delta, delta); } timers_state.qemu_icount_bias += warp_delta; + check_clock = true; } vm_clock_warp_start = -1; seqlock_write_unlock(&timers_state.vm_clock_seqlock); - if (qemu_clock_expired(QEMU_CLOCK_VIRTUAL)) { + if (check_clock && qemu_clock_expired(QEMU_CLOCK_VIRTUAL)) { qemu_clock_notify(QEMU_CLOCK_VIRTUAL); } } -- 2.7.3