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bh=broKGiBHn4Mrcqhd26WBYkZyDDh8lM2XHC1mQBH7Muc=; b=TEAGEHYzOJGrklKbYqx31UC0AGRTjkBxkyM/SMWJD37gx4b+faqgIbD5NBAZtYcxEYFENe kGWEBsuChdHm2X7mxF1lGdyzTE7H4zbnEeW8nuOL8NjoOZ+whPlGiJiByaGn5BTk8AIGDn c2A8qGgBXv9cfhqFcMRQVCFv/HjvOyA= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-230-6fWx9KHnNkGwh-LiHpM-HQ-1; Wed, 09 Jun 2021 12:13:01 -0400 X-MC-Unique: 6fWx9KHnNkGwh-LiHpM-HQ-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 2E573185060A; Wed, 9 Jun 2021 16:13:00 +0000 (UTC) Received: from starship (unknown [10.40.194.6]) by smtp.corp.redhat.com (Postfix) with ESMTP id 05CD55D9C6; Wed, 9 Jun 2021 16:12:56 +0000 (UTC) Message-ID: <9378247cb67d5b1afe7f4d83fab22a16ed610ae3.camel@redhat.com> Subject: Re: [PATCH v4 3/7] block: add max_hw_transfer to BlockLimits From: Maxim Levitsky To: Paolo Bonzini , qemu-devel@nongnu.org Date: Wed, 09 Jun 2021 19:12:55 +0300 In-Reply-To: <20210608131634.423904-4-pbonzini@redhat.com> References: <20210608131634.423904-1-pbonzini@redhat.com> <20210608131634.423904-4-pbonzini@redhat.com> User-Agent: Evolution 3.36.5 (3.36.5-2.fc32) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=mlevitsk@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=170.10.133.124; envelope-from=mlevitsk@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -29 X-Spam_score: -3.0 X-Spam_bar: --- X-Spam_report: (-3.0 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.199, 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_H4=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: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: kwolf@redhat.com, vsementsov@virtuozzo.com, Max Reitz , qemu-block@nongnu.org, Tom Yan Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Tue, 2021-06-08 at 15:16 +0200, Paolo Bonzini wrote: > For block host devices, I/O can happen through either the kernel file > descriptor I/O system calls (preadv/pwritev, io_submit, io_uring) > or the SCSI passthrough ioctl SG_IO. > > In the latter case, the size of each transfer can be limited by the > HBA, while for file descriptor I/O the kernel is able to split and > merge I/O in smaller pieces as needed. Applying the HBA limits to > file descriptor I/O results in more system calls and suboptimal > performance, so this patch splits the max_transfer limit in two: > max_transfer remains valid and is used in general, while max_hw_transfer > is limited to the maximum hardware size. max_hw_transfer can then be > included by the scsi-generic driver in the block limits page, to ensure > that the stricter hardware limit is used. > > Signed-off-by: Paolo Bonzini This is mostly the same as my patch https://www.mail-archive.com/qemu-devel@nongnu.org/msg768264.html I called this max_ioctl_transfer, since this limit is only relevant to the .ioctl, but max_hw_transfer is fine as well. So this patch looks OK, but I might have missed something as I haven't touched this area for a long time. Reviewed-by: Maxim Levitsky Best regards, Maxim Levitsky > --- > block/block-backend.c | 12 ++++++++++++ > block/file-posix.c | 2 +- > block/io.c | 1 + > hw/scsi/scsi-generic.c | 2 +- > include/block/block_int.h | 7 +++++++ > include/sysemu/block-backend.h | 1 + > 6 files changed, 23 insertions(+), 2 deletions(-) > > diff --git a/block/block-backend.c b/block/block-backend.c > index 15f1ea4288..2ea1412a54 100644 > --- a/block/block-backend.c > +++ b/block/block-backend.c > @@ -1953,6 +1953,18 @@ uint32_t blk_get_request_alignment(BlockBackend *blk) > return bs ? bs->bl.request_alignment : BDRV_SECTOR_SIZE; > } > > +/* Returns the maximum hardware transfer length, in bytes; guaranteed nonzero */ > +uint64_t blk_get_max_hw_transfer(BlockBackend *blk) > +{ > + BlockDriverState *bs = blk_bs(blk); > + uint64_t max = INT_MAX; > + > + if (bs) { > + max = MIN_NON_ZERO(bs->bl.max_hw_transfer, bs->bl.max_transfer); > + } > + return max; > +} > + > /* Returns the maximum transfer length, in bytes; guaranteed nonzero */ > uint32_t blk_get_max_transfer(BlockBackend *blk) > { > diff --git a/block/file-posix.c b/block/file-posix.c > index 670c577bfe..c9746d3eb6 100644 > --- a/block/file-posix.c > +++ b/block/file-posix.c > @@ -1234,7 +1234,7 @@ static void raw_refresh_limits(BlockDriverState *bs, Error **errp) > int ret = sg_get_max_transfer_length(s->fd); > > if (ret > 0 && ret <= BDRV_REQUEST_MAX_BYTES) { > - bs->bl.max_transfer = pow2floor(ret); > + bs->bl.max_hw_transfer = pow2floor(ret); > } > > ret = sg_get_max_segments(s->fd); > diff --git a/block/io.c b/block/io.c > index 323854d063..089b99bb0c 100644 > --- a/block/io.c > +++ b/block/io.c > @@ -127,6 +127,7 @@ static void bdrv_merge_limits(BlockLimits *dst, const BlockLimits *src) > { > dst->opt_transfer = MAX(dst->opt_transfer, src->opt_transfer); > dst->max_transfer = MIN_NON_ZERO(dst->max_transfer, src->max_transfer); > + dst->max_hw_transfer = MIN_NON_ZERO(dst->max_hw_transfer, src->max_hw_transfer); > dst->opt_mem_alignment = MAX(dst->opt_mem_alignment, > src->opt_mem_alignment); > dst->min_mem_alignment = MAX(dst->min_mem_alignment, > diff --git a/hw/scsi/scsi-generic.c b/hw/scsi/scsi-generic.c > index 82e1e2ee79..3762dce749 100644 > --- a/hw/scsi/scsi-generic.c > +++ b/hw/scsi/scsi-generic.c > @@ -179,7 +179,7 @@ static void scsi_handle_inquiry_reply(SCSIGenericReq *r, SCSIDevice *s) > (r->req.cmd.buf[1] & 0x01)) { > page = r->req.cmd.buf[2]; > if (page == 0xb0) { > - uint32_t max_transfer = blk_get_max_transfer(s->conf.blk); > + uint64_t max_transfer = blk_get_max_hw_transfer(s->conf.blk); > uint32_t max_iov = blk_get_max_iov(s->conf.blk); > > assert(max_transfer); > diff --git a/include/block/block_int.h b/include/block/block_int.h > index 057d88b1fc..f1a54db0f8 100644 > --- a/include/block/block_int.h > +++ b/include/block/block_int.h > @@ -695,6 +695,13 @@ typedef struct BlockLimits { > * clamped down. */ > uint32_t max_transfer; > > + /* Maximal hardware transfer length in bytes. Applies whenever > + * transfers to the device bypass the kernel I/O scheduler, for > + * example with SG_IO. If larger than max_transfer or if zero, > + * blk_get_max_hw_transfer will fall back to max_transfer. > + */ > + uint64_t max_hw_transfer; > + > /* memory alignment, in bytes so that no bounce buffer is needed */ > size_t min_mem_alignment; > > diff --git a/include/sysemu/block-backend.h b/include/sysemu/block-backend.h > index 5423e3d9c6..9ac5f7bbd3 100644 > --- a/include/sysemu/block-backend.h > +++ b/include/sysemu/block-backend.h > @@ -208,6 +208,7 @@ void blk_eject(BlockBackend *blk, bool eject_flag); > int blk_get_flags(BlockBackend *blk); > uint32_t blk_get_request_alignment(BlockBackend *blk); > uint32_t blk_get_max_transfer(BlockBackend *blk); > +uint64_t blk_get_max_hw_transfer(BlockBackend *blk); > int blk_get_max_iov(BlockBackend *blk); > void blk_set_guest_block_size(BlockBackend *blk, int align); > void *blk_try_blockalign(BlockBackend *blk, size_t size);