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<1617854972.35808055.1574323227395.JavaMail.zimbra@redhat.com> <560894997.35969622.1574397521533.JavaMail.zimbra@redhat.com> Subject: Re: [PATCH] virtio pmem: fix async flush ordering MIME-Version: 1.0 X-Originating-IP: [10.67.116.214, 10.4.195.30] Thread-Topic: virtio pmem: fix async flush ordering Thread-Index: yct1AVHQcm+1LDSyVVEj51GYlhrF5A== X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-MC-Unique: T_UOHI-YNQGQjE4f7guipw-1 X-Mimecast-Spam-Score: 0 Message-ID-Hash: CLYO7P5M4NIZGUV6YFFP4YUYZHVIMDTF X-Message-ID-Hash: CLYO7P5M4NIZGUV6YFFP4YUYZHVIMDTF X-MailFrom: pagupta@redhat.com X-Mailman-Rule-Misses: dmarc-mitigation; no-senders; approved; emergency; loop; banned-address; member-moderation; nonmember-moderation; administrivia; implicit-dest; max-recipients; max-size; news-moderation; no-subject; suspicious-header CC: linux-nvdimm , Linux Kernel Mailing List , Linux ACPI , "Rafael J. Wysocki" , Len Brown X-Mailman-Version: 3.1.1 Precedence: list List-Id: "Linux-nvdimm developer list." Archived-At: List-Archive: List-Help: List-Post: List-Subscribe: List-Unsubscribe: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit > > > > > > > > > > > > I added that and was about to push this out, but what about the > > > > > > fact > > > > > > that now the guest will synchronously wait for flushing to occur. > > > > > > The > > > > > > goal of the child bio was to allow that to be an I/O wait with > > > > > > overlapping I/O, or at least not blocking the submission thread. > > > > > > Does > > > > > > the block layer synchronously wait for PREFLUSH requests? If not I > > > > > > think a synchronous wait is going to be a significant performance > > > > > > regression. Are there any numbers to accompany this change? > > > > > > > > > > Why not just swap the parent child relationship in the PREFLUSH case? > > > > > > > > I we are already inside parent bio "make_request" function and we > > > > create > > > > child > > > > bio. How we exactly will swap the parent/child relationship for > > > > PREFLUSH > > > > case? > > > > > > > > Child bio is queued after parent bio completes. > > > > > > Sorry, I didn't quite mean with bio_split, but issuing another request > > > in front of the real bio. See md_flush_request() for inspiration. > > > > o.k. Thank you. Will try to post patch today to be considered for 5.4. > > > > I think it is too late for v5.4-final, but we can get it in the > -stable queue. Let's take the time to do it right and get some testing > on it. Sure. Just sharing probable patch for early feedback, if I am doing it correctly? I will test it thoroughly. Thanks, Pankaj ======== diff --git a/drivers/nvdimm/nd_virtio.c b/drivers/nvdimm/nd_virtio.c index 10351d5b49fa..c683e0e2515c 100644 --- a/drivers/nvdimm/nd_virtio.c +++ b/drivers/nvdimm/nd_virtio.c @@ -112,6 +112,12 @@ int async_pmem_flush(struct nd_region *nd_region, struct bio *bio) bio_copy_dev(child, bio); child->bi_opf = REQ_PREFLUSH; child->bi_iter.bi_sector = -1; + + if (unlikely(bio->bi_opf & REQ_PREFLUSH)) { + struct request_queue *q = bio->bi_disk->queue; + q->make_request_fn(q, child); + return 0; + } bio_chain(child, bio); submit_bio(child); return 0; _______________________________________________ Linux-nvdimm mailing list -- linux-nvdimm@lists.01.org To unsubscribe send an email to linux-nvdimm-leave@lists.01.org