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=-15.1 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,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 59BC6C07E95 for ; Tue, 20 Jul 2021 14:10:11 +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 CE58161186 for ; Tue, 20 Jul 2021 14:10:10 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org CE58161186 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:51652 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1m5qRl-0006mS-Tg for qemu-devel@archiver.kernel.org; Tue, 20 Jul 2021 10:10:09 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:37706) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1m5qQd-0005ke-C7 for qemu-devel@nongnu.org; Tue, 20 Jul 2021 10:08:59 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:60655) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1m5qQZ-0004yc-6I for qemu-devel@nongnu.org; Tue, 20 Jul 2021 10:08:57 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1626790133; h=from:from:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:in-reply-to:in-reply-to: references:references; bh=I6W2Gszz0YhUW8Fr95rlhqoiuGUipmINIJKr/9DWPJ0=; b=R0LdUUb109Yi7QlDsiEXT58T3b9LfHpftvjPdcGXL5CYT1cJmXjqkkStgCOObAx0ncoHGS lrOwXVxbHeM9f6eZKjl97/N5D+kYtQUXNnUu+Xso7tOdQpMJ9FG2Yf5caXx9jHFHQFOUfa OAwydTeK7t/yyi1g9JzXa+4AcIGkjgc= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-526-Np_LYoyNMDO6jrqOCGlVjQ-1; Tue, 20 Jul 2021 10:08:48 -0400 X-MC-Unique: Np_LYoyNMDO6jrqOCGlVjQ-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 345708030D7; Tue, 20 Jul 2021 14:08:47 +0000 (UTC) Received: from redhat.com (ovpn-113-31.ams2.redhat.com [10.36.113.31]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 4B4755C1CF; Tue, 20 Jul 2021 14:08:37 +0000 (UTC) Date: Tue, 20 Jul 2021 15:08:35 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: David Hildenbrand Subject: Re: [PATCH v1 1/3] util/oslib-posix: Support MADV_POPULATE_WRITE for os_mem_prealloc() Message-ID: References: <20210714112306.67793-1-david@redhat.com> <20210714112306.67793-2-david@redhat.com> MIME-Version: 1.0 In-Reply-To: <20210714112306.67793-2-david@redhat.com> User-Agent: Mutt/2.0.7 (2021-05-04) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=berrange@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Received-SPF: pass client-ip=170.10.133.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -42 X-Spam_score: -4.3 X-Spam_bar: ---- X-Spam_report: (-4.3 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1.474, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=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: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Cc: Pankaj Gupta , Eduardo Habkost , "Michael S. Tsirkin" , qemu-devel@nongnu.org, "Dr . David Alan Gilbert" , Paolo Bonzini , Igor Mammedov , Marek Kedzierski Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Wed, Jul 14, 2021 at 01:23:04PM +0200, David Hildenbrand wrote: > Let's sense support and use it for preallocation. MADV_POPULATE_WRITE > does not require a SIGBUS handler, doesn't actually touch page content, > and avoids context switches; it is, therefore, faster and easier to handle > than our current approach. > > This resolves the TODO in do_touch_pages(). > > Signed-off-by: David Hildenbrand > --- > include/qemu/osdep.h | 7 ++++ > util/oslib-posix.c | 84 +++++++++++++++++++++++++++++++++----------- > 2 files changed, 71 insertions(+), 20 deletions(-) > > diff --git a/util/oslib-posix.c b/util/oslib-posix.c > index e8bdb02e1d..679796ac1f 100644 > --- a/util/oslib-posix.c > +++ b/util/oslib-posix.c > @@ -484,10 +484,6 @@ static void *do_touch_pages(void *arg) > * > * 'volatile' to stop compiler optimizing this away > * to a no-op > - * > - * TODO: get a better solution from kernel so we > - * don't need to write at all so we don't cause > - * wear on the storage backing the region... > */ > *(volatile char *)addr = *addr; > addr += hpagesize; > @@ -497,6 +493,27 @@ static void *do_touch_pages(void *arg) > return NULL; > } > > +static void *do_madv_populate_write_pages(void *arg) > +{ > + MemsetThread *memset_args = (MemsetThread *)arg; > + const size_t size = memset_args->numpages * memset_args->hpagesize; > + char * const addr = memset_args->addr; > + int ret; > + > + /* See do_touch_pages(). */ > + qemu_mutex_lock(&page_mutex); > + while (!threads_created_flag) { > + qemu_cond_wait(&page_cond, &page_mutex); > + } > + qemu_mutex_unlock(&page_mutex); > + > + ret = qemu_madvise(addr, size, QEMU_MADV_POPULATE_WRITE); > + if (ret) { > + memset_thread_failed = true; > + } > + return NULL; > +} > + > static inline int get_memset_num_threads(int smp_cpus) > { > long host_procs = sysconf(_SC_NPROCESSORS_ONLN); > @@ -510,10 +527,11 @@ static inline int get_memset_num_threads(int smp_cpus) > } > > static bool touch_all_pages(char *area, size_t hpagesize, size_t numpages, > - int smp_cpus) > + int smp_cpus, bool use_madv_populate_write) > { > static gsize initialized = 0; > size_t numpages_per_thread, leftover; > + void *(*touch_fn)(void *); > char *addr = area; > int i = 0; > > @@ -523,6 +541,12 @@ static bool touch_all_pages(char *area, size_t hpagesize, size_t numpages, > g_once_init_leave(&initialized, 1); > } > > + if (use_madv_populate_write) { > + touch_fn = do_madv_populate_write_pages; > + } else { > + touch_fn = do_touch_pages; > + } > + > memset_thread_failed = false; > threads_created_flag = false; > memset_num_threads = get_memset_num_threads(smp_cpus); > @@ -534,7 +558,7 @@ static bool touch_all_pages(char *area, size_t hpagesize, size_t numpages, > memset_thread[i].numpages = numpages_per_thread + (i < leftover); > memset_thread[i].hpagesize = hpagesize; > qemu_thread_create(&memset_thread[i].pgthread, "touch_pages", > - do_touch_pages, &memset_thread[i], > + touch_fn, &memset_thread[i], > QEMU_THREAD_JOINABLE); > addr += memset_thread[i].numpages * hpagesize; > } Do you have an indication of what the speed differential is for the old read/write dance vs the kernel madvise. We needed to use threads previously because the read/write dance is pretty terribly slow. Is that still a problem with the madvise approach ? I would (perhaps naively), expect that the kernel would be able to do this efficiently for arbitrarily large memory regions, such that QEMU would not need to play games with threads. > @@ -553,6 +577,12 @@ static bool touch_all_pages(char *area, size_t hpagesize, size_t numpages, > return memset_thread_failed; > } > > +static bool madv_populate_write_possible(char *area, size_t pagesize) > +{ > + return !qemu_madvise(area, pagesize, QEMU_MADV_POPULATE_WRITE) || > + errno != EINVAL; > +} > + > void os_mem_prealloc(int fd, char *area, size_t memory, int smp_cpus, > Error **errp) > { > @@ -560,29 +590,43 @@ void os_mem_prealloc(int fd, char *area, size_t memory, int smp_cpus, > struct sigaction act, oldact; > size_t hpagesize = qemu_fd_getpagesize(fd); > size_t numpages = DIV_ROUND_UP(memory, hpagesize); > + bool use_madv_populate_write; Initialized with random garbage from the stack > + > + /* > + * Sense on every invocation, as MADV_POPULATE_WRITE cannot be used for > + * some special mappings, such as mapping /dev/mem. > + */ > + if (madv_populate_write_possible(area, hpagesize)) { > + use_madv_populate_write = true; > + } but this implicitly assumes it was initialized to false. > > - memset(&act, 0, sizeof(act)); > - act.sa_handler = &sigbus_handler; > - act.sa_flags = 0; > + if (!use_madv_populate_write) { > + memset(&act, 0, sizeof(act)); > + act.sa_handler = &sigbus_handler; > + act.sa_flags = 0; > > - ret = sigaction(SIGBUS, &act, &oldact); > - if (ret) { > - error_setg_errno(errp, errno, > - "os_mem_prealloc: failed to install signal handler"); > - return; > + ret = sigaction(SIGBUS, &act, &oldact); > + if (ret) { > + error_setg_errno(errp, errno, > + "os_mem_prealloc: failed to install signal handler"); > + return; > + } > } > > /* touch pages simultaneously */ > - if (touch_all_pages(area, hpagesize, numpages, smp_cpus)) { > + if (touch_all_pages(area, hpagesize, numpages, smp_cpus, > + use_madv_populate_write)) { > error_setg(errp, "os_mem_prealloc: Insufficient free host memory " > "pages available to allocate guest RAM"); > } > > - ret = sigaction(SIGBUS, &oldact, NULL); > - if (ret) { > - /* Terminate QEMU since it can't recover from error */ > - perror("os_mem_prealloc: failed to reinstall signal handler"); > - exit(1); > + if (!use_madv_populate_write) { > + ret = sigaction(SIGBUS, &oldact, NULL); > + if (ret) { > + /* Terminate QEMU since it can't recover from error */ > + perror("os_mem_prealloc: failed to reinstall signal handler"); > + exit(1); > + } > } > } > > -- > 2.31.1 > > Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|