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 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 smtp.lore.kernel.org (Postfix) with ESMTPS id D90F4C77B75 for ; Fri, 5 May 2023 07:20:02 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1pupio-0002aq-9a; Fri, 05 May 2023 03:19:18 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1pupil-0002a1-HB for qemu-devel@nongnu.org; Fri, 05 May 2023 03:19:16 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1pupij-0003x8-JK for qemu-devel@nongnu.org; Fri, 05 May 2023 03:19:15 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1683271151; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=RZntnz5WyXfqZSraaxuRb8+Sihb9+Z6wHXC5gCDecz0=; b=LcuCLnD7hdXeks3rMuo7SzjCfpIeRwtD2/1aM0HqEcnxvrgzjDv9NY+1wffQaGXArY8W90 izKxy0z2gqx4BN0B/TbUNd49RWDDedAol+0XD1n3O0PbipC3iLFJU47jI6CCiUxLv6nATF 8NBxMbMBgRz/bGzeCxyzlDW+rLNlXzY= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-435-tCntgJ84PQ6DtQM2pKAt_A-1; Fri, 05 May 2023 03:19:08 -0400 X-MC-Unique: tCntgJ84PQ6DtQM2pKAt_A-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.rdu2.redhat.com [10.11.54.8]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 9A0AE1006E27; Fri, 5 May 2023 07:19:07 +0000 (UTC) Received: from redhat.com (unknown [10.42.28.42]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 80EDBC15BA0; Fri, 5 May 2023 07:19:06 +0000 (UTC) Date: Fri, 5 May 2023 08:19:04 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Juan Quintela Cc: qemu-devel@nongnu.org, qemu-block@nongnu.org, Stefan Hajnoczi , Leonardo Bras , Fam Zheng , Peter Xu Subject: Re: [PATCH 9/9] qemu-file: Account for rate_limit usage on qemu_fflush() Message-ID: References: <20230504113841.23130-1-quintela@redhat.com> <20230504113841.23130-10-quintela@redhat.com> <87h6ssovu6.fsf@secure.mitica> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <87h6ssovu6.fsf@secure.mitica> User-Agent: Mutt/2.2.9 (2022-11-12) X-Scanned-By: MIMEDefang 3.1 on 10.11.54.8 Received-SPF: pass client-ip=170.10.129.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -22 X-Spam_score: -2.3 X-Spam_bar: -- X-Spam_report: (-2.3 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.161, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=unavailable autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Thu, May 04, 2023 at 07:22:25PM +0200, Juan Quintela wrote: > Daniel P. Berrangé wrote: > > On Thu, May 04, 2023 at 01:38:41PM +0200, Juan Quintela wrote: > >> That is the moment we know we have transferred something. > >> > >> Signed-off-by: Juan Quintela > >> --- > >> migration/qemu-file.c | 7 +++---- > >> 1 file changed, 3 insertions(+), 4 deletions(-) > >> > >> diff --git a/migration/qemu-file.c b/migration/qemu-file.c > >> index ddebfac847..309b4c56f4 100644 > >> --- a/migration/qemu-file.c > >> +++ b/migration/qemu-file.c > >> @@ -300,7 +300,9 @@ void qemu_fflush(QEMUFile *f) > >> &local_error) < 0) { > >> qemu_file_set_error_obj(f, -EIO, local_error); > >> } else { > >> - f->total_transferred += iov_size(f->iov, f->iovcnt); > >> + uint64_t size = iov_size(f->iov, f->iovcnt); > >> + qemu_file_acct_rate_limit(f, size); > >> + f->total_transferred += size; > >> } > >> > >> qemu_iovec_release_ram(f); > >> @@ -527,7 +529,6 @@ void qemu_put_buffer_async(QEMUFile *f, const uint8_t *buf, size_t size, > >> return; > >> } > >> > >> - f->rate_limit_used += size; > >> add_to_iovec(f, buf, size, may_free); > >> } > >> > >> @@ -545,7 +546,6 @@ void qemu_put_buffer(QEMUFile *f, const uint8_t *buf, size_t size) > >> l = size; > >> } > >> memcpy(f->buf + f->buf_index, buf, l); > >> - f->rate_limit_used += l; > >> add_buf_to_iovec(f, l); > >> if (qemu_file_get_error(f)) { > >> break; > >> @@ -562,7 +562,6 @@ void qemu_put_byte(QEMUFile *f, int v) > >> } > >> > >> f->buf[f->buf_index] = v; > >> - f->rate_limit_used++; > >> add_buf_to_iovec(f, 1); > >> } > > > > This has a slight semantic behavioural change. > > Yeap. > > See the answer to Peter. But three things came to mind: > > a - the size of the buffer is small (between 32KB and 256KB depending > how you count it). So we are going to call qemu_fflush() really > soon. > > b - We are using this value to calculate how much we can send through > the wire. Here we are saything how much we have accepted to send. > > c - When using multifd the number of bytes that we send through the qemu > file is even smaller. migration-test multifd test send 300MB of data > through multifd channels and around 300KB on the qemu_file channel. > > > > > > By accounting for rate limit in the qemu_put functions, we ensure > > that we stop growing the iovec when rate limiting activates. > > > > If we only apply rate limit in the the flush function, that will > > let the f->iov continue to accumulate buffers, while we have > > rate limited the actual transfer. > > 256KB maximum. Our accounting has bigger errors than that. > > > > This makes me uneasy - it feels like a bad idea to continue to > > accumulate buffers if we're not ready to send them > > I still think that the change is correct. But as you and Peter have > concerns about it, I will think a bit more about it. If Peter's calculations are correct, then I don't have any objection, as that's a small overhead. With 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 :|