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=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 33EADC3A5A2 for ; Tue, 3 Sep 2019 13:23:02 +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 0A2FC215EA for ; Tue, 3 Sep 2019 13:23:02 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0A2FC215EA 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]:46030 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1i58lx-0000I8-99 for qemu-devel@archiver.kernel.org; Tue, 03 Sep 2019 09:23:01 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:50166) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1i58lB-0007wB-PS for qemu-devel@nongnu.org; Tue, 03 Sep 2019 09:22:15 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1i58lA-00078R-2W for qemu-devel@nongnu.org; Tue, 03 Sep 2019 09:22:13 -0400 Received: from mx1.redhat.com ([209.132.183.28]:49708) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1i58l9-00077v-QO for qemu-devel@nongnu.org; Tue, 03 Sep 2019 09:22:12 -0400 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id D3CD33082133; Tue, 3 Sep 2019 13:22:10 +0000 (UTC) Received: from work-vm (unknown [10.36.118.29]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 7C6D95D6B2; Tue, 3 Sep 2019 13:22:09 +0000 (UTC) Date: Tue, 3 Sep 2019 14:22:07 +0100 From: "Dr. David Alan Gilbert" To: Wei Yang Message-ID: <20190903132207.GH2744@work-vm> References: <20190731144225.3784-1-richardw.yang@linux.intel.com> <20190731144225.3784-3-richardw.yang@linux.intel.com> <20190823110609.GF2784@work-vm> <20190823113801.GF9654@redhat.com> <20190823130502.GH2784@work-vm> <20190824162216.ypo6vp2c6u2om4o7@master> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190824162216.ypo6vp2c6u2om4o7@master> User-Agent: Mutt/1.12.1 (2019-06-15) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.42]); Tue, 03 Sep 2019 13:22:10 +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: , Cc: qemu-devel@nongnu.org, "Daniel P. Berrang?" , Wei Yang , quintela@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" * Wei Yang (richard.weiyang@gmail.com) wrote: > On Fri, Aug 23, 2019 at 02:05:02PM +0100, Dr. David Alan Gilbert wrote: > >* Daniel P. Berrang? (berrange@redhat.com) wrote: > >> 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. > > > >No, there's two separate types of buffers. > > > >There's f->buf which is a single allocated buffer in the QEMUFile > >with an offset buf_index, and there are arbitrary RAM pages > >added typically via qemu_put_buffer_async. > > > > qemu_put_buffer_async is the only one which put a range not in f->buf into the > iovec. > > And one thing confused me is even its name is async, add_to_iovec still would > call qemu_fflush when iovec is full. So it is not a always async function. > From the function name, it is a little difficult to differentiate > qemu_put_buffer and qemu_put_buffer_async. It's a bit confusing, but I think it is the right name; the 'async' refers to the fact that the data is read from the buffer we pass sometime later, not synchronously before the return of the qemu_put_buffer_async call. Dave > >The check for >= IO_BUF_SIZE is only done when adding to the f->buf, > >where as the check on f->iovcnt is done when you add an element to > >the iovec and that can happen potentially in either case. > > > >Dave > > > >> 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 :| > >-- > >Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK > > -- > Wei Yang > Help you, Help me -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK