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Thu, 13 Jan 2022 13:06:02 +0000 (UTC) Received: from redhat.com (unknown [10.33.37.41]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 09BA8105C728; Thu, 13 Jan 2022 13:05:50 +0000 (UTC) Date: Thu, 13 Jan 2022 13:05:48 +0000 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Leonardo Bras Subject: Re: [PATCH v7 2/5] QIOChannelSocket: Implement io_writev zero copy flag & io_flush for CONFIG_LINUX Message-ID: References: <20220106221341.8779-1-leobras@redhat.com> <20220106221341.8779-3-leobras@redhat.com> MIME-Version: 1.0 In-Reply-To: <20220106221341.8779-3-leobras@redhat.com> User-Agent: Mutt/2.1.3 (2021-09-10) X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 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 Content-Transfer-Encoding: 8bit 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: -33 X-Spam_score: -3.4 X-Spam_bar: --- X-Spam_report: (-3.4 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.594, 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_H3=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: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Cc: Juan Quintela , qemu-devel@nongnu.org, Peter Xu , Markus Armbruster , Eric Blake , "Dr. David Alan Gilbert" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Thu, Jan 06, 2022 at 07:13:39PM -0300, Leonardo Bras wrote: > For CONFIG_LINUX, implement the new zero copy flag and the optional callback > io_flush on QIOChannelSocket, but enables it only when MSG_ZEROCOPY > feature is available in the host kernel, which is checked on > qio_channel_socket_connect_sync() > > qio_channel_socket_flush() was implemented by counting how many times > sendmsg(...,MSG_ZEROCOPY) was successfully called, and then reading the > socket's error queue, in order to find how many of them finished sending. > Flush will loop until those counters are the same, or until some error occurs. > > Notes on using writev() with QIO_CHANNEL_WRITE_FLAG_ZERO_COPY: > 1: Buffer > - As MSG_ZEROCOPY tells the kernel to use the same user buffer to avoid copying, > some caution is necessary to avoid overwriting any buffer before it's sent. > If something like this happen, a newer version of the buffer may be sent instead. > - If this is a problem, it's recommended to call qio_channel_flush() before freeing > or re-using the buffer. > > 2: Locked memory > - When using MSG_ZERCOCOPY, the buffer memory will be locked after queued, and > unlocked after it's sent. > - Depending on the size of each buffer, and how often it's sent, it may require > a larger amount of locked memory than usually available to non-root user. > - If the required amount of locked memory is not available, writev_zero_copy > will return an error, which can abort an operation like migration, > - Because of this, when an user code wants to add zero copy as a feature, it > requires a mechanism to disable it, so it can still be accessible to less > privileged users. > > Signed-off-by: Leonardo Bras > --- > include/io/channel-socket.h | 2 + > io/channel-socket.c | 107 ++++++++++++++++++++++++++++++++++-- > 2 files changed, 105 insertions(+), 4 deletions(-) Reviewed-by: Daniel P. Berrangé 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 :|