From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:47385) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1YQeQA-0002PY-9g for qemu-devel@nongnu.org; Wed, 25 Feb 2015 11:02:46 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1YQeQ8-0006pN-Lo for qemu-devel@nongnu.org; Wed, 25 Feb 2015 11:02:46 -0500 Received: from static.88-198-71-155.clients.your-server.de ([88.198.71.155]:47128 helo=socrates.bennee.com) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1YQeQ8-0006oV-G6 for qemu-devel@nongnu.org; Wed, 25 Feb 2015 11:02:44 -0500 From: =?UTF-8?q?Alex=20Benn=C3=A9e?= Date: Wed, 25 Feb 2015 16:02:35 +0000 Message-Id: <1424880159-29348-4-git-send-email-alex.bennee@linaro.org> In-Reply-To: <1424880159-29348-1-git-send-email-alex.bennee@linaro.org> References: <1424880159-29348-1-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 3/6] hw/char/pl011: don't keep setting the IRQ if nothing changed List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Cc: kvm@vger.kernel.org, marc.zyngier@arm.com, linux-arm-kernel@lists.infradead.org, =?UTF-8?q?Alex=20Benn=C3=A9e?= , kvmarm@lists.cs.columbia.edu, christoffer.dall@linaro.org While observing KVM traces I can see additional IRQ calls on pretty much every MMIO access which is just plain inefficient. Only update the QEMU IRQ level if something has actually changed from last time. Otherwise we may be papering over other failure modes. Signed-off-by: Alex Bennée diff --git a/hw/char/pl011.c b/hw/char/pl011.c index 0a45115..bb554bc 100644 --- a/hw/char/pl011.c +++ b/hw/char/pl011.c @@ -36,6 +36,9 @@ typedef struct PL011State { CharDriverState *chr; qemu_irq irq; const unsigned char *id; + + /* not serialised, prevents pl011_update doing extra set_irqs */ + uint32_t current_irq; } PL011State; #define PL011_INT_TX 0x20 @@ -53,10 +56,11 @@ static const unsigned char pl011_id_luminary[8] = static void pl011_update(PL011State *s) { - uint32_t flags; - - flags = s->int_level & s->int_enabled; - qemu_set_irq(s->irq, flags != 0); + uint32_t flags = s->int_level & s->int_enabled; + if (flags != s->current_irq) { + s->current_irq = flags; + qemu_set_irq(s->irq, s->current_irq != 0); + } } static uint64_t pl011_read(void *opaque, hwaddr offset, -- 2.3.0