From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:56079) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1cWjhT-0000Km-3b for qemu-devel@nongnu.org; Thu, 26 Jan 2017 08:02:52 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1cWjhP-0006mK-T3 for qemu-devel@nongnu.org; Thu, 26 Jan 2017 08:02:51 -0500 Received: from mail-wm0-x243.google.com ([2a00:1450:400c:c09::243]:33991) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_128_CBC_SHA1:16) (Exim 4.71) (envelope-from ) id 1cWjhP-0006ly-Mh for qemu-devel@nongnu.org; Thu, 26 Jan 2017 08:02:47 -0500 Received: by mail-wm0-x243.google.com with SMTP id c85so50170024wmi.1 for ; Thu, 26 Jan 2017 05:02:47 -0800 (PST) Sender: Paolo Bonzini References: <20170126123411.5412.44769.stgit@PASHA-ISP> <20170126123423.5412.2388.stgit@PASHA-ISP> From: Paolo Bonzini Message-ID: <06b49612-9faf-5933-d8e9-8645a2fcde4d@redhat.com> Date: Thu, 26 Jan 2017 14:02:45 +0100 MIME-Version: 1.0 In-Reply-To: <20170126123423.5412.2388.stgit@PASHA-ISP> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Subject: Re: [Qemu-devel] [PATCH v8 2/9] icount: exit cpu loop on expire List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Pavel Dovgalyuk , qemu-devel@nongnu.org Cc: kwolf@redhat.com, peter.maydell@linaro.org, quintela@redhat.com, jasowang@redhat.com, mst@redhat.com, kraxel@redhat.com On 26/01/2017 13:34, Pavel Dovgalyuk wrote: > This patch adds check to break cpu loop when icount expires without > setting the TB_EXIT_ICOUNT_EXPIRED flag. It happens when there is no > available translated blocks and all instructions were executed. > In icount replay mode unnecessary tb_find will be called (which may > cause an exception) and execution will be non-deterministic. > > v8: refactored loop exit code and moved it to separate function > > Signed-off-by: Pavel Dovgalyuk > --- > cpu-exec.c | 24 +++++++++++++++++++----- > 1 file changed, 19 insertions(+), 5 deletions(-) > > diff --git a/cpu-exec.c b/cpu-exec.c > index fa08c73..f9b8ec8 100644 > --- a/cpu-exec.c > +++ b/cpu-exec.c > @@ -523,9 +523,25 @@ static inline void cpu_handle_interrupt(CPUState *cpu, > *last_tb = NULL; > } > } > - if (unlikely(atomic_read(&cpu->exit_request) || replay_has_interrupt())) { > +} > + > + > +static void cpu_check_loop_exit(CPUState *cpu) > +{ > + if (unlikely(atomic_read(&cpu->exit_request) > + /* icount has expired, we need to break the execution loop. > + This check is needed before tb_find to make execution > + deterministic - tb_find may cause an exception > + while translating the code from non-mapped page. */ > + || (use_icount && ((cpu->icount_extra == 0 > + && cpu->icount_decr.u16.low == 0) > + || (int32_t)cpu->icount_decr.u32 < 0)))) { Simpler: use_icount && ((int32_t)cpu->icount_decr.u32 < 0 || cpu->icount_decr.low + cpu->icount_extra == 0) But I'm not sure that you need to test u32. After all you're not testing tcg_exit_req, which is the equivalent when icount is disabled. > atomic_set(&cpu->exit_request, 0); > - cpu->exception_index = EXCP_INTERRUPT; > + /* If there is an exception that wasn't replayed yet, > + don't change exception_index. */ > + if (cpu->exception_index == -1) { > + cpu->exception_index = EXCP_INTERRUPT; > + } > cpu_loop_exit(cpu); The siglongjmp is effectively the same as exiting the for(;;) loop of cpu_exec and going back to cpu_handle_exception. So I would just merge this with cpu_handle_interrupt, which exits a lot with cpu_loop_exit too. All cpu_loop_exit() calls in cpu_handle_interrupt become "return true", similar to cpu_handle_exception, and then in cpu_exec you have: /* if an exception is pending, we execute it here */ while (!cpu_handle_exception(cpu, &ret)) { /* if an interrupt is pending, inject it and go back * to cpu_handle_exception. */ while (!cpu_handle_interrupt(cpu, &last_tb)) { tb = tb_find(cpu, last_tb, tb_exit); cpu_loop_exec_tb(cpu, tb, &last_tb, &tb_exit, &sc); /* Try to align the host and virtual clocks if the guest is in advance */ align_clocks(&sc, cpu); } } break; > #endif > @@ -634,6 +647,7 @@ int cpu_exec(CPUState *cpu) > > for(;;) { > cpu_handle_interrupt(cpu, &last_tb); > + cpu_check_loop_exit(cpu); if (cpu_should_check_exception_or_exit(cpu)) { break; } > tb = tb_find(cpu, last_tb, tb_exit); > cpu_loop_exec_tb(cpu, tb, &last_tb, &tb_exit, &sc); > /* Try to align the host and virtual clocks > > >