From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 00B4B24DD09 for ; Mon, 9 Jun 2025 09:02:55 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.133.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1749459777; cv=none; b=tfOK03xy0LWT4HkU37CnNMy4xm1yskQ55pB7WeWsEoVsF53pCdjR3vkBd4KbQL8dzJ3nPMLzui2tVHM1fCofx4yECHAhcf422h5x5AzfOIdVfHxeLnJi6d58nAqNnGBKN3HyRvnvjn0RGLPrcvcdfPzRyKNcebo3BJ7Kou4rHKE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1749459777; c=relaxed/simple; bh=XXEa42Xq99wKOLyfd3oZa9Jua01KyvdxLYvYUkAsIy8=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=KH28THZcqctmUOlYQOvnBuapjxNGXdxEUpGHeA4cK4oPItaKCZSvq+deQWXOtQrI75hbvWbUygeoZtuv1S0ljNJdC9rgdiJJrEwdA/j3zRGpcbyWzV5CZOtngXQnNiNnzaucYsDcf4KmEbx2Ds6c9drRR/hjeUcxZvewHZtz3Gk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=ZxJKUESh; arc=none smtp.client-ip=170.10.133.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="ZxJKUESh" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1749459775; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=+c1SrI/vIeGZwZ0yUBpAnS8UHNagHMOkcglrCyVMyGc=; b=ZxJKUEShSB8MW4oermxbxi5G9vUzwcKau4kP5JiwGCH974w4rf8gAlgal3/tZGa0Jh/IWl ezC8dKb3jJRGDsglDTPPHedxdb+fsv7mepvZSHqEdrpimfg2EI6+iLwnPcZvtHPmLnNRcH O2MnIudaWV/FPyfbn7BuM7LG0ogIwuU= Received: from mx-prod-mc-06.mail-002.prod.us-west-2.aws.redhat.com (ec2-35-165-154-97.us-west-2.compute.amazonaws.com [35.165.154.97]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-622-grEep_8hNYenl41mz-i9Vw-1; Mon, 09 Jun 2025 05:02:51 -0400 X-MC-Unique: grEep_8hNYenl41mz-i9Vw-1 X-Mimecast-MFC-AGG-ID: grEep_8hNYenl41mz-i9Vw_1749459770 Received: from mx-prod-int-04.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-04.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.40]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id E5E241800289; Mon, 9 Jun 2025 09:02:49 +0000 (UTC) Received: from fedora (unknown [10.72.116.58]) by mx-prod-int-04.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 54A3319560AB; Mon, 9 Jun 2025 09:02:45 +0000 (UTC) Date: Mon, 9 Jun 2025 17:02:41 +0800 From: Ming Lei To: Caleb Sander Mateos Cc: Uday Shankar , linux-block@vger.kernel.org Subject: Re: [PATCH 7/8] ublk: optimize UBLK_IO_REGISTER_IO_BUF on daemon task Message-ID: References: <20250606214011.2576398-1-csander@purestorage.com> <20250606214011.2576398-8-csander@purestorage.com> Precedence: bulk X-Mailing-List: linux-block@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250606214011.2576398-8-csander@purestorage.com> X-Scanned-By: MIMEDefang 3.0 on 10.30.177.40 On Fri, Jun 06, 2025 at 03:40:10PM -0600, Caleb Sander Mateos wrote: > ublk_register_io_buf() performs an expensive atomic refcount increment, > as well as a lot of pointer chasing to look up the struct request. > > Create a separate ublk_daemon_register_io_buf() for the daemon task to > call. Initialize ublk_rq_data's reference count to a large number, count > the number of buffers registered on the daemon task nonatomically, and > atomically subtract the large number minus the number of registered > buffers in ublk_commit_and_fetch(). > > Also obtain the struct request directly from ublk_io's req field instead > of looking it up on the tagset. > > Signed-off-by: Caleb Sander Mateos > --- > drivers/block/ublk_drv.c | 59 ++++++++++++++++++++++++++++++++++------ > 1 file changed, 50 insertions(+), 9 deletions(-) > > diff --git a/drivers/block/ublk_drv.c b/drivers/block/ublk_drv.c > index 2084bbdd2cbb..ec9e0fd21b0e 100644 > --- a/drivers/block/ublk_drv.c > +++ b/drivers/block/ublk_drv.c > @@ -81,12 +81,20 @@ > #define UBLK_PARAM_TYPE_ALL \ > (UBLK_PARAM_TYPE_BASIC | UBLK_PARAM_TYPE_DISCARD | \ > UBLK_PARAM_TYPE_DEVT | UBLK_PARAM_TYPE_ZONED | \ > UBLK_PARAM_TYPE_DMA_ALIGN | UBLK_PARAM_TYPE_SEGMENT) > > +/* > + * Initialize refcount to a large number to include any registered buffers. > + * UBLK_IO_COMMIT_AND_FETCH_REQ will release these references minus those for > + * any buffers registered on the io daemon task. > + */ > +#define UBLK_REFCOUNT_INIT (REFCOUNT_MAX / 2) > + > struct ublk_rq_data { > refcount_t ref; > + unsigned buffers_registered; > > /* for auto-unregister buffer in case of UBLK_F_AUTO_BUF_REG */ > u16 buf_index; > void *buf_ctx_handle; > }; > @@ -677,11 +685,12 @@ static inline void ublk_init_req_ref(const struct ublk_queue *ubq, > struct request *req) > { > if (ublk_need_req_ref(ubq)) { > struct ublk_rq_data *data = blk_mq_rq_to_pdu(req); > > - refcount_set(&data->ref, 1); > + refcount_set(&data->ref, UBLK_REFCOUNT_INIT); > + data->buffers_registered = 0; > } > } > > static inline bool ublk_get_req_ref(const struct ublk_queue *ubq, > struct request *req) > @@ -706,10 +715,19 @@ static inline void ublk_put_req_ref(const struct ublk_queue *ubq, > } else { > __ublk_complete_rq(req); > } > } > > +static inline void ublk_sub_req_ref(struct request *req) > +{ > + struct ublk_rq_data *data = blk_mq_rq_to_pdu(req); > + unsigned sub_refs = UBLK_REFCOUNT_INIT - data->buffers_registered; > + > + if (refcount_sub_and_test(sub_refs, &data->ref)) > + __ublk_complete_rq(req); > +} > + > static inline bool ublk_need_get_data(const struct ublk_queue *ubq) > { > return ubq->flags & UBLK_F_NEED_GET_DATA; > } > > @@ -1184,14 +1202,12 @@ static inline void __ublk_abort_rq(struct ublk_queue *ubq, > > static void ublk_auto_buf_reg_fallback(struct request *req) > { > const struct ublk_queue *ubq = req->mq_hctx->driver_data; > struct ublksrv_io_desc *iod = ublk_get_iod(ubq, req->tag); > - struct ublk_rq_data *data = blk_mq_rq_to_pdu(req); > > iod->op_flags |= UBLK_IO_F_NEED_REG_BUF; > - refcount_set(&data->ref, 1); > } > > static bool ublk_auto_buf_reg(struct request *req, struct ublk_io *io, > unsigned int issue_flags) > { > @@ -1207,13 +1223,12 @@ static bool ublk_auto_buf_reg(struct request *req, struct ublk_io *io, > return true; > } > blk_mq_end_request(req, BLK_STS_IOERR); > return false; > } > - /* one extra reference is dropped by ublk_io_release */ > - refcount_set(&data->ref, 2); > > + data->buffers_registered = 1; > data->buf_ctx_handle = io_uring_cmd_ctx_handle(io->cmd); > /* store buffer index in request payload */ > data->buf_index = pdu->buf.index; > io->flags |= UBLK_IO_FLAG_AUTO_BUF_REG; > return true; > @@ -1221,14 +1236,14 @@ static bool ublk_auto_buf_reg(struct request *req, struct ublk_io *io, > > static bool ublk_prep_auto_buf_reg(struct ublk_queue *ubq, > struct request *req, struct ublk_io *io, > unsigned int issue_flags) > { > + ublk_init_req_ref(ubq, req); > if (ublk_support_auto_buf_reg(ubq) && ublk_rq_has_data(req)) > return ublk_auto_buf_reg(req, io, issue_flags); > > - ublk_init_req_ref(ubq, req); > return true; > } > > static bool ublk_start_io(const struct ublk_queue *ubq, struct request *req, > struct ublk_io *io) > @@ -2019,10 +2034,31 @@ static int ublk_register_io_buf(struct io_uring_cmd *cmd, > } > > return 0; > } > > +static int ublk_daemon_register_io_buf(struct io_uring_cmd *cmd, > + const struct ublk_queue *ubq, > + const struct ublk_io *io, > + unsigned index, unsigned issue_flags) > +{ > + struct request *req = io->req; > + struct ublk_rq_data *data = blk_mq_rq_to_pdu(req); > + int ret; > + > + if (!ublk_support_zero_copy(ubq) || !ublk_rq_has_data(req)) > + return -EINVAL; > + > + ret = io_buffer_register_bvec(cmd, req, ublk_io_release, index, > + issue_flags); > + if (ret) > + return ret; > + > + data->buffers_registered++; This optimization replaces one ublk_get_req_ref()/refcount_inc_not_zero() with data->buffers_registered++ in case of registering io buffer from daemon context. And in typical implementation, the unregistering io buffer should be done in daemon context too, then I am wondering if any user-visible improvement can be observed in this more complicated & fragile way: - __ublk_check_and_get_req() is bypassed. - buggy application may overflow ->buffers_registered So can you share any data about this optimization on workload with local registering & remote un-registering io buffer? Also is this usage really one common case? Thanks, Ming