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Wed, 3 Jul 2019 15:28:07 +0000 (UTC) Message-ID: From: Maxim Levitsky To: Eric Blake , qemu-devel@nongnu.org Date: Wed, 03 Jul 2019 18:28:06 +0300 In-Reply-To: <70330e00-ebe9-ce2a-5155-6f7e032e0aae@redhat.com> References: <20190630150855.1016-1-mlevitsk@redhat.com> <20190630150855.1016-2-mlevitsk@redhat.com> <70330e00-ebe9-ce2a-5155-6f7e032e0aae@redhat.com> Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.45]); Wed, 03 Jul 2019 15:28:09 +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 1/1] raw-posix.c - use max transfer length / max segemnt count only for SCSI passthrough 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: Fam Zheng , Kevin Wolf , Max Reitz , qemu-block@nongnu.org, John Ferlan Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Wed, 2019-07-03 at 09:50 -0500, Eric Blake wrote: > On 6/30/19 10:08 AM, Maxim Levitsky wrote: > > Regular block devices (/dev/sda*, /dev/nvme*, etc) interface is not limited > > The regular block device interface is > > or > > Regular block devices interfaces are > > > by the underlying storage limits, but rather the kernel block layer > > takes care to split the requests that are too large/fragmented. > > > > Doing so allows us to have less overhead in qemu. > > > > Signed-off-by: Maxim Levitsky > > --- > > block/file-posix.c | 16 +++++++--------- > > 1 file changed, 7 insertions(+), 9 deletions(-) > > > > diff --git a/block/file-posix.c b/block/file-posix.c > > index ab05b51a66..66dad34f8a 100644 > > --- a/block/file-posix.c > > +++ b/block/file-posix.c > > @@ -1038,15 +1038,13 @@ static void raw_reopen_abort(BDRVReopenState *state) > > s->reopen_state = NULL; > > } > > > > -static int hdev_get_max_transfer_length(BlockDriverState *bs, int fd) > > +static int sg_get_max_transfer_length(BlockDriverState *bs, int fd) > > { > > #ifdef BLKSECTGET > > int max_bytes = 0; > > - short max_sectors = 0; > > - if (bs->sg && ioctl(fd, BLKSECTGET, &max_bytes) == 0) { > > + > > + if (ioctl(fd, BLKSECTGET, &max_bytes) == 0) { > > return max_bytes; > > - } else if (!bs->sg && ioctl(fd, BLKSECTGET, &max_sectors) == 0) { > > - return max_sectors << BDRV_SECTOR_BITS; > > } else { > > return -errno; > > } > > @@ -1055,7 +1053,7 @@ static int hdev_get_max_transfer_length(BlockDriverState *bs, int fd) > > #endif > > } > > > > -static int hdev_get_max_segments(const struct stat *st) > > +static int sg_get_max_segments(const struct stat *st) > > { > > #ifdef CONFIG_LINUX > > char buf[32]; > > @@ -1106,12 +1104,12 @@ static void raw_refresh_limits(BlockDriverState *bs, Error **errp) > > struct stat st; > > > > if (!fstat(s->fd, &st)) { > > - if (S_ISBLK(st.st_mode) || S_ISCHR(st.st_mode)) { > > - int ret = hdev_get_max_transfer_length(bs, s->fd); > > Is it worth delaying the fstat()... > > > + if (bs->sg) { > > + int ret = sg_get_max_transfer_length(bs, s->fd); > > if (ret > 0 && ret <= BDRV_REQUEST_MAX_BYTES) { > > bs->bl.max_transfer = pow2floor(ret); > > } > > - ret = hdev_get_max_segments(&st); > > + ret = sg_get_max_segments(&st); > > ...until inside the if (bs->sg) condition, to avoid wasted work for > other scenarios? > > > if (ret > 0) { > > bs->bl.max_transfer = MIN(bs->bl.max_transfer, > > ret * getpagesize()); > > > > Reviewed-by: Eric Blake > Thank you very much for the review. I'll send a V2 soon. Best regards, Maxim Levitsky