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=-8.2 required=3.0 tests=FROM_EXCESS_BASE64, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, 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 6C502C3A5A2 for ; Fri, 23 Aug 2019 11:39:29 +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 42C4F21848 for ; Fri, 23 Aug 2019 11:39:29 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 42C4F21848 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]:54188 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1i17ui-0008Bw-G9 for qemu-devel@archiver.kernel.org; Fri, 23 Aug 2019 07:39:28 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:47890) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1i17tX-0007ZC-1K for qemu-devel@nongnu.org; Fri, 23 Aug 2019 07:38:16 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1i17tV-00067s-7N for qemu-devel@nongnu.org; Fri, 23 Aug 2019 07:38:14 -0400 Received: from mx1.redhat.com ([209.132.183.28]:56914) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1i17tU-00065U-85 for qemu-devel@nongnu.org; Fri, 23 Aug 2019 07:38:12 -0400 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id DA09F30860BA; Fri, 23 Aug 2019 11:38:09 +0000 (UTC) Received: from redhat.com (ovpn-112-60.ams2.redhat.com [10.36.112.60]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 65677600CD; Fri, 23 Aug 2019 11:38:04 +0000 (UTC) Date: Fri, 23 Aug 2019 12:38:01 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: "Dr. David Alan Gilbert" Message-ID: <20190823113801.GF9654@redhat.com> References: <20190731144225.3784-1-richardw.yang@linux.intel.com> <20190731144225.3784-3-richardw.yang@linux.intel.com> <20190823110609.GF2784@work-vm> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20190823110609.GF2784@work-vm> User-Agent: Mutt/1.12.0 (2019-05-25) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.44]); Fri, 23 Aug 2019 11:38:10 +0000 (UTC) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 209.132.183.28 Subject: Re: [Qemu-devel] [PATCH 2/2] migration/qemu-file: fix potential buf waste for extra buf_index adjustment 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: quintela@redhat.com, Wei Yang , qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Fri, Aug 23, 2019 at 12:06:09PM +0100, Dr. David Alan Gilbert wrote: > (Copying Dan in) > > * Wei Yang (richardw.yang@linux.intel.com) wrote: > > In add_to_iovec(), qemu_fflush() will be called if iovec is full. If > > this happens, buf_index is reset. Currently, this is not checked and > > buf_index would always been adjust with buf size. > > > > This is not harmful, but will waste some space in file buffer. > > That's a nice find. > > > This patch make add_to_iovec() return 1 when it has flushed the file. > > Then the caller could check the return value to see whether it is > > necessary to adjust the buf_index any more. > > > > Signed-off-by: Wei Yang > > Reviewed-by: Dr. David Alan Gilbert > > (I wonder if there's a way to wrap that little add_to_iovec, check, add > to index, flush in a little wrapper). Given the name "add_to_iovec" I think it is pretty surprising that it calls "qemu_flush" at all. It is also pretty wierd that we're checking two different conditions in two different places. Right now the code is essentially doing this: if (f->iovcnt >= MAX_IOV_SIZE) { qemu_fflush(f); } if (f->buf_index == IO_BUF_SIZE) { qemu_fflush(f); } Except that in the qemu_put_buffer_async() case, we're only doing the first of these two checks. This feels very odd indeed - I would have thought either it should do both, or do neither. Assuming doing both flushs is ok for qemu_put_buffer_async then I'd suggest renaming 'add_to_iovec' to 'queue_buffer' and have that method do both of these qemu_fflush() calls. > > --- > > migration/qemu-file.c | 42 ++++++++++++++++++++++++++++-------------- > > 1 file changed, 28 insertions(+), 14 deletions(-) > > > > diff --git a/migration/qemu-file.c b/migration/qemu-file.c > > index 35c22605dd..05d9f42ddb 100644 > > --- a/migration/qemu-file.c > > +++ b/migration/qemu-file.c > > @@ -343,8 +343,16 @@ int qemu_fclose(QEMUFile *f) > > return ret; > > } > > > > -static void add_to_iovec(QEMUFile *f, const uint8_t *buf, size_t size, > > - bool may_free) > > +/* > > + * Add buf to iovec. Do flush if iovec is full. > > + * > > + * Return values: > > + * 1 iovec is full and flushed > > + * 0 iovec is not flushed > > + * > > + */ > > +static int add_to_iovec(QEMUFile *f, const uint8_t *buf, size_t size, > > + bool may_free) > > { > > /* check for adjacent buffer and coalesce them */ > > if (f->iovcnt > 0 && buf == f->iov[f->iovcnt - 1].iov_base + > > @@ -362,7 +370,10 @@ static void add_to_iovec(QEMUFile *f, const uint8_t *buf, size_t size, > > > > if (f->iovcnt >= MAX_IOV_SIZE) { > > qemu_fflush(f); > > + return 1; > > } > > + > > + return 0; > > } > > > > void qemu_put_buffer_async(QEMUFile *f, const uint8_t *buf, size_t size, > > @@ -391,10 +402,11 @@ void qemu_put_buffer(QEMUFile *f, const uint8_t *buf, size_t size) > > } > > memcpy(f->buf + f->buf_index, buf, l); > > f->bytes_xfer += l; > > - add_to_iovec(f, f->buf + f->buf_index, l, false); > > - f->buf_index += l; > > - if (f->buf_index == IO_BUF_SIZE) { > > - qemu_fflush(f); > > + if (!add_to_iovec(f, f->buf + f->buf_index, l, false)) { > > + f->buf_index += l; > > + if (f->buf_index == IO_BUF_SIZE) { > > + qemu_fflush(f); > > + } > > } > > if (qemu_file_get_error(f)) { > > break; > > @@ -412,10 +424,11 @@ void qemu_put_byte(QEMUFile *f, int v) > > > > f->buf[f->buf_index] = v; > > f->bytes_xfer++; > > - add_to_iovec(f, f->buf + f->buf_index, 1, false); > > - f->buf_index++; > > - if (f->buf_index == IO_BUF_SIZE) { > > - qemu_fflush(f); > > + if (!add_to_iovec(f, f->buf + f->buf_index, 1, false)) { > > + f->buf_index++; > > + if (f->buf_index == IO_BUF_SIZE) { > > + qemu_fflush(f); > > + } > > } > > } > > > > @@ -717,10 +730,11 @@ ssize_t qemu_put_compression_data(QEMUFile *f, z_stream *stream, > > } > > > > qemu_put_be32(f, blen); > > - add_to_iovec(f, f->buf + f->buf_index, blen, false); > > - f->buf_index += blen; > > - if (f->buf_index == IO_BUF_SIZE) { > > - qemu_fflush(f); > > + if (!add_to_iovec(f, f->buf + f->buf_index, blen, false)) { > > + f->buf_index += blen; > > + if (f->buf_index == IO_BUF_SIZE) { > > + qemu_fflush(f); > > + } > > } > > return blen + sizeof(int32_t); > > } > > -- > > 2.17.1 > > > -- > Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK > 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 :|