From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1INvlJ-0007n6-EF for qemu-devel@nongnu.org; Wed, 22 Aug 2007 15:21:05 -0400 Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43) id 1INvlH-0007mr-3W for qemu-devel@nongnu.org; Wed, 22 Aug 2007 15:21:04 -0400 Received: from [199.232.76.173] (helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1INvlG-0007mo-U3 for qemu-devel@nongnu.org; Wed, 22 Aug 2007 15:21:02 -0400 Received: from rv-out-0910.google.com ([209.85.198.184]) by monty-python.gnu.org with esmtp (Exim 4.60) (envelope-from ) id 1INvlG-0003Ag-HY for qemu-devel@nongnu.org; Wed, 22 Aug 2007 15:21:02 -0400 Received: by rv-out-0910.google.com with SMTP id c27so234874rvf for ; Wed, 22 Aug 2007 12:21:01 -0700 (PDT) Message-ID: <68676e00708221221n6f8fcd67m9d15f7fea663ec71@mail.gmail.com> Date: Wed, 22 Aug 2007 21:21:01 +0200 From: Luca In-Reply-To: <68676e00708221023m352c2de3y3b19188dbb9ef49e@mail.gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Content-Disposition: inline References: <20070817231149.544849769@gmail.com> <20070820212058.GA6713@dreamland.darkstar.lan> <46CAD607.2080504@qumranet.com> <20070821193834.GB13544@dreamland.darkstar.lan> <46CBC34F.6060601@qumranet.com> <20070822161211.GA30147@dreamland.darkstar.lan> <46CC6285.3090904@qumranet.com> <68676e00708220938y57c07edas705fc8360aefcb78@mail.gmail.com> <46CC680C.1030307@qumranet.com> <68676e00708221023m352c2de3y3b19188dbb9ef49e@mail.gmail.com> Subject: [Qemu-devel] Re: [kvm-devel] [PATCH 0/4] Rework alarm timer infrastrucure - take2 Reply-To: qemu-devel@nongnu.org List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Avi Kivity Cc: Dan Kenigsberg , kvm-devel@lists.sf.net, qemu-devel@nongnu.org On 8/22/07, Luca wrote: > On 8/22/07, Avi Kivity wrote: > > Luca wrote: > > >>> This is QEMU, with dynticks and HPET: > > >>> > > >>> % time seconds usecs/call calls errors syscall > > >>> ------ ----------- ----------- --------- --------- ---------------- > > >>> 52.10 0.002966 0 96840 clock_gettime > > >>> 19.50 0.001110 0 37050 timer_gettime > > >>> 10.66 0.000607 0 20086 timer_settime > > >>> 10.40 0.000592 0 8985 2539 sigreturn > > >>> 4.94 0.000281 0 8361 2485 select > > >>> 2.41 0.000137 0 8362 gettimeofday > > >>> ------ ----------- ----------- --------- --------- ---------------- > > >>> 100.00 0.005693 179684 5024 total > > >>> > > >>> > > >> This looks like 250 Hz? > > >> > > > > > > Nope: > > > > > > # CONFIG_NO_HZ is not set > > > # CONFIG_HZ_100 is not set > > > # CONFIG_HZ_250 is not set > > > # CONFIG_HZ_300 is not set > > > CONFIG_HZ_1000=y > > > CONFIG_HZ=1000 > > > > > > and I'm reading it from /proc/config.gz on the guest. > > > > > > > Yeah, thought so -- so dyntick is broken at present. > > I see a lot of sub ms timer_settime(). Many of them are the result of > ->expire_time being less than the current qemu_get_clock(). This > results into 250us timer due to MIN_TIMER_REARM_US; this happens only > for the REALTIME timer. Other sub-ms timers are generated by the > VIRTUAL timer. > > This first issue is easily fixed; if expire_time < current time then > the timer has expired and hasn't been reprogrammed (and thus can be > ignored). > VIRTUAL just becomes more accurate with dyntics, before multiple > timers were batched together. > > > Or maybe your host kernel can't support such a high rate. > > I don't know... a simple printf tells me that the signal handler is > called about 1050 times per second, which sounds about right. ...unless strace is attached. ptrace()'ing the process really screw up the timing with dynticks; HPET is also affected but the performance hit is not as severe. Luca