From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-15.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id C211DC64E7A for ; Tue, 1 Dec 2020 23:15:02 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id D88342220B for ; Tue, 1 Dec 2020 23:15:01 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D88342220B Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=csgraf.de Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:58570 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1kkErM-0005ym-JT for qemu-devel@archiver.kernel.org; Tue, 01 Dec 2020 18:15:00 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:53978) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1kkEpq-0004s3-7T; Tue, 01 Dec 2020 18:13:26 -0500 Received: from mail.csgraf.de ([188.138.100.120]:53502 helo=zulu616.server4you.de) by eggs.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1kkEpg-000817-Sb; Tue, 01 Dec 2020 18:13:25 -0500 Received: from freeip.amazon.com (ec2-3-122-114-9.eu-central-1.compute.amazonaws.com [3.122.114.9]) by csgraf.de (Postfix) with UTF8SMTPSA id E57C1390038F; Wed, 2 Dec 2020 00:13:12 +0100 (CET) Subject: Re: [PATCH] arm/hvf: Optimize and simplify WFI handling From: Alexander Graf To: Peter Collingbourne References: <20201201082142.649007-1-pcc@google.com> <5b691ccb-43bb-5955-d47a-cae39c59522c@csgraf.de> <8cc9052b-da85-de93-9d54-d4d0730054ec@csgraf.de> Message-ID: <835a98b6-e108-7479-489e-6c5d8d00408d@csgraf.de> Date: Wed, 2 Dec 2020 00:13:12 +0100 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.16; rv:84.0) Gecko/20100101 Thunderbird/84.0 MIME-Version: 1.0 In-Reply-To: <8cc9052b-da85-de93-9d54-d4d0730054ec@csgraf.de> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US Received-SPF: pass client-ip=188.138.100.120; envelope-from=agraf@csgraf.de; helo=zulu616.server4you.de X-Spam_score_int: -18 X-Spam_score: -1.9 X-Spam_bar: - X-Spam_report: (-1.9 / 5.0 requ) BAYES_00=-1.9, NICE_REPLY_A=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Peter Maydell , Eduardo Habkost , Richard Henderson , qemu-devel , Cameron Esfahani , Roman Bolshakov , qemu-arm@nongnu.org, Claudio Fontana , Frank Yang , Paolo Bonzini Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 01.12.20 23:09, Alexander Graf wrote: > > On 01.12.20 21:03, Peter Collingbourne wrote: >> On Tue, Dec 1, 2020 at 8:26 AM Alexander Graf wrote: >>> >>> On 01.12.20 09:21, Peter Collingbourne wrote: >>>> Sleep on WFx until the VTIMER is due but allow ourselves to be woken >>>> up on IPI. >>>> >>>> Signed-off-by: Peter Collingbourne >>>> --- >>>> Alexander Graf wrote: >>>>> I would love to take a patch from you here :). I'll still be stuck >>>>> for a >>>>> while with the sysreg sync rework that Peter asked for before I >>>>> can look >>>>> at WFI again. >>>> Okay, here's a patch :) It's a relatively straightforward adaptation >>>> of what we have in our fork, which can now boot Android to GUI while >>>> remaining at around 4% CPU when idle. >>>> >>>> I'm not set up to boot a full Linux distribution at the moment so I >>>> tested it on upstream QEMU by running a recent mainline Linux kernel >>>> with a rootfs containing an init program that just does sleep(5) >>>> and verified that the qemu process remains at low CPU usage during >>>> the sleep. This was on top of your v2 plus the last patch of your v1 >>>> since it doesn't look like you have a replacement for that logic yet. >>> >>> How about something like this instead? >>> >>> >>> Alex >>> >>> >>> diff --git a/accel/hvf/hvf-cpus.c b/accel/hvf/hvf-cpus.c >>> index 4360f64671..50384013ea 100644 >>> --- a/accel/hvf/hvf-cpus.c >>> +++ b/accel/hvf/hvf-cpus.c >>> @@ -337,16 +337,18 @@ static int hvf_init_vcpu(CPUState *cpu) >>>        cpu->hvf = g_malloc0(sizeof(*cpu->hvf)); >>> >>>        /* init cpu signals */ >>> -    sigset_t set; >>>        struct sigaction sigact; >>> >>>        memset(&sigact, 0, sizeof(sigact)); >>>        sigact.sa_handler = dummy_signal; >>>        sigaction(SIG_IPI, &sigact, NULL); >>> >>> -    pthread_sigmask(SIG_BLOCK, NULL, &set); >>> -    sigdelset(&set, SIG_IPI); >>> -    pthread_sigmask(SIG_SETMASK, &set, NULL); >>> +    pthread_sigmask(SIG_BLOCK, NULL, &cpu->hvf->sigmask); >>> +    sigdelset(&cpu->hvf->sigmask, SIG_IPI); >>> +    pthread_sigmask(SIG_SETMASK, &cpu->hvf->sigmask, NULL); >>> + >>> +    pthread_sigmask(SIG_BLOCK, NULL, &cpu->hvf->sigmask_ipi); >>> +    sigaddset(&cpu->hvf->sigmask_ipi, SIG_IPI); >> There's no reason to unblock SIG_IPI while not in pselect and it can >> easily lead to missed wakeups. The whole point of pselect is so that >> you can guarantee that only one part of your program sees signals >> without a possibility of them being missed. > > > Hm, I think I start to agree with you here :). We can probably just > leave SIG_IPI masked at all times and only unmask on pselect. The > worst thing that will happen is a premature wakeup if we did get an > IPI incoming while hvf->sleeping is set, but were either not running > pselect() yet and bailed out or already finished pselect() execution. How about this one? Do you really think it's still racy? Alex diff --git a/accel/hvf/hvf-cpus.c b/accel/hvf/hvf-cpus.c index 4360f64671..e10fca622d 100644 --- a/accel/hvf/hvf-cpus.c +++ b/accel/hvf/hvf-cpus.c @@ -337,16 +337,17 @@ static int hvf_init_vcpu(CPUState *cpu)      cpu->hvf = g_malloc0(sizeof(*cpu->hvf));      /* init cpu signals */ -    sigset_t set;      struct sigaction sigact;      memset(&sigact, 0, sizeof(sigact));      sigact.sa_handler = dummy_signal;      sigaction(SIG_IPI, &sigact, NULL); -    pthread_sigmask(SIG_BLOCK, NULL, &set); -    sigdelset(&set, SIG_IPI); -    pthread_sigmask(SIG_SETMASK, &set, NULL); +    /* Remember unmasked IPI mask for pselect(), leave masked normally */ +    pthread_sigmask(SIG_BLOCK, NULL, &cpu->hvf->sigmask_ipi); +    sigaddset(&cpu->hvf->sigmask_ipi, SIG_IPI); +    pthread_sigmask(SIG_SETMASK, &cpu->hvf->sigmask_ipi, NULL); +    sigdelset(&cpu->hvf->sigmask_ipi, SIG_IPI);  #ifdef __aarch64__      r = hv_vcpu_create(&cpu->hvf->fd, (hv_vcpu_exit_t **)&cpu->hvf->exit, NULL); diff --git a/include/sysemu/hvf_int.h b/include/sysemu/hvf_int.h index c56baa3ae8..8d7d4a6226 100644 --- a/include/sysemu/hvf_int.h +++ b/include/sysemu/hvf_int.h @@ -62,8 +62,8 @@ extern HVFState *hvf_state;  struct hvf_vcpu_state {      uint64_t fd;      void *exit; -    struct timespec ts;      bool sleeping; +    sigset_t sigmask_ipi;  };  void assert_hvf_ok(hv_return_t ret); diff --git a/target/arm/hvf/hvf.c b/target/arm/hvf/hvf.c index 0c01a03725..a255a1a7d3 100644 --- a/target/arm/hvf/hvf.c +++ b/target/arm/hvf/hvf.c @@ -320,14 +320,8 @@ int hvf_arch_init_vcpu(CPUState *cpu)  void hvf_kick_vcpu_thread(CPUState *cpu)  { -    if (cpu->hvf->sleeping) { -        /* -         * When sleeping, make sure we always send signals. Also, clear the -         * timespec, so that an IPI that arrives between setting hvf->sleeping -         * and the nanosleep syscall still aborts the sleep. -         */ -        cpu->thread_kicked = false; -        cpu->hvf->ts = (struct timespec){ }; +    if (qatomic_read(&cpu->hvf->sleeping)) { +        /* When sleeping, send a signal to get out of pselect */          cpus_kick_thread(cpu);      } else {          hv_vcpus_exit(&cpu->hvf->fd, 1); @@ -354,6 +348,7 @@ int hvf_vcpu_exec(CPUState *cpu)      ARMCPU *arm_cpu = ARM_CPU(cpu);      CPUARMState *env = &arm_cpu->env;      hv_vcpu_exit_t *hvf_exit = cpu->hvf->exit; +    const uint32_t irq_mask = CPU_INTERRUPT_HARD | CPU_INTERRUPT_FIQ;      hv_return_t r;      int ret = 0; @@ -491,8 +486,8 @@ int hvf_vcpu_exec(CPUState *cpu)              break;          }          case EC_WFX_TRAP: -            if (!(syndrome & WFX_IS_WFE) && !(cpu->interrupt_request & -                (CPU_INTERRUPT_HARD | CPU_INTERRUPT_FIQ))) { +            if (!(syndrome & WFX_IS_WFE) && +                !(cpu->interrupt_request & irq_mask)) {                  uint64_t cval, ctl, val, diff, now;                  /* Set up a local timer for vtimer if necessary ... */ @@ -515,9 +510,7 @@ int hvf_vcpu_exec(CPUState *cpu)                  if (diff < INT64_MAX) {                      uint64_t ns = diff * gt_cntfrq_period_ns(arm_cpu); -                    struct timespec *ts = &cpu->hvf->ts; - -                    *ts = (struct timespec){ +                    struct timespec ts = {                          .tv_sec = ns / NANOSECONDS_PER_SECOND,                          .tv_nsec = ns % NANOSECONDS_PER_SECOND,                      }; @@ -526,27 +519,27 @@ int hvf_vcpu_exec(CPUState *cpu)                       * Waking up easily takes 1ms, don't go to sleep for smaller                       * time periods than 2ms.                       */ -                    if (!ts->tv_sec && (ts->tv_nsec < (SCALE_MS * 2))) { +                    if (!ts.tv_sec && (ts.tv_nsec < (SCALE_MS * 2))) {                          advance_pc = true;                          break;                      } +                    cpu->thread_kicked = false; +                      /* Set cpu->hvf->sleeping so that we get a SIG_IPI signal. */ -                    cpu->hvf->sleeping = true; -                    smp_mb(); +                    qatomic_set(&cpu->hvf->sleeping, true); -                    /* Bail out if we received an IRQ meanwhile */ -                    if (cpu->thread_kicked || (cpu->interrupt_request & -                        (CPU_INTERRUPT_HARD | CPU_INTERRUPT_FIQ))) { -                        cpu->hvf->sleeping = false; +                    /* Bail out if we received a kick meanwhile */ +                    if (qatomic_read(&cpu->interrupt_request) & irq_mask) { + qatomic_set(&cpu->hvf->sleeping, false);                          break;                      } -                    /* nanosleep returns on signal, so we wake up on kick. */ -                    nanosleep(ts, NULL); +                    /* pselect returns on kick signal and consumes it */ +                    pselect(0, 0, 0, 0, &ts, &cpu->hvf->sigmask_ipi);                      /* Out of sleep - either naturally or because of a kick */ -                    cpu->hvf->sleeping = false; +                    qatomic_set(&cpu->hvf->sleeping, false);                  }                  advance_pc = true;