From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:43548) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1VPbEH-00089R-LA for qemu-devel@nongnu.org; Fri, 27 Sep 2013 12:49:27 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1VPbEC-0004RD-7l for qemu-devel@nongnu.org; Fri, 27 Sep 2013 12:49:21 -0400 Message-ID: <5245B70E.6050105@weilnetz.de> Date: Fri, 27 Sep 2013 18:49:18 +0200 From: Stefan Weil MIME-Version: 1.0 References: <1378910555-24753-1-git-send-email-stefanha@redhat.com> <52451595.1000506@weilnetz.de> <20130927091107.GA9972@stefanha-thinkpad.redhat.com> In-Reply-To: <20130927091107.GA9972@stefanha-thinkpad.redhat.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH] coroutine: add ./configure --disable-coroutine-pool List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Stefan Hajnoczi Cc: Kevin Wolf , gabriel@kerneis.info, qemu-devel@nongnu.org, qemu-stable Am 27.09.2013 11:11, schrieb Stefan Hajnoczi: > On Fri, Sep 27, 2013 at 07:20:21AM +0200, Stefan Weil wrote: >> Am 11.09.2013 16:42, schrieb Stefan Hajnoczi: >>> The 'gthread' coroutine backend was written before the freelist (aka >>> pool) existed in qemu-coroutine.c. >>> >>> This means that every thread is expected to exit when its coroutine >>> terminates. It is not possible to reuse threads from a pool. >>> >>> This patch automatically disables the pool when 'gthread' is used. This >>> allows the 'gthread' backend to work again (for example, >>> tests/test-coroutine completes successfully instead of hanging). >>> >>> I considered implementing thread reuse but I don't want quirks like CPU >>> affinity differences due to coroutine threads being recycled. The >>> 'gthread' backend is a reference backend and it's therefore okay to skip >>> the pool optimization. >>> >>> Note this patch also makes it easy to toggle the pool for benchmarking >>> purposes: >>> >>> ./configure --with-coroutine-backend=ucontext \ >>> --disable-coroutine-pool >>> >>> Reported-by: Gabriel Kerneis >>> Signed-off-by: Stefan Hajnoczi >>> --- >>> configure | 24 ++++++++++++++++++++++++ >>> qemu-coroutine.c | 34 +++++++++++++++++++--------------- >>> 2 files changed, 43 insertions(+), 15 deletions(-) >>> >> This patch is important for QEMU 1.5 as well, but needs some >> modifications there. >> A recent bug report for MinGW shows that the win32 coroutine needs it, too. > coroutine-win32.c is designed to support reuse: > > static void CALLBACK coroutine_trampoline(void *co_) > { > Coroutine *co = co_; > > while (true) { > co->entry(co->entry_arg); > qemu_coroutine_switch(co, co->caller, COROUTINE_TERMINATE); > } > } > > We return from qemu_coroutine_switch() when the fiber is reused and > simply run another iteration of the while loop. > > Why do you say win32 coroutines should disable the pool? > > Stefan QEMU MinGW binaries with coroutine pool simply crash, and disabling the pool helps for the moment until we have a better fix. That's a regression which was introduced with a patch which added the pool for win32. See this discussion thread for more details: http://lists.nongnu.org/archive/html/qemu-devel/2013-09/msg04195.html Regards, Stefan