From owner-dev-commits-src-all@freebsd.org Sat Jul 31 00:21:31 2021 Return-Path: Delivered-To: dev-commits-src-all@mailman.nyi.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1]) by mailman.nyi.freebsd.org (Postfix) with ESMTP id 28A29651423; Sat, 31 Jul 2021 00:21:31 +0000 (UTC) (envelope-from git@FreeBSD.org) Received: from mxrelay.nyi.freebsd.org (mxrelay.nyi.freebsd.org [IPv6:2610:1c1:1:606c::19:3]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256 client-signature RSA-PSS (4096 bits) client-digest SHA256) (Client CN "mxrelay.nyi.freebsd.org", Issuer "R3" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id 4Gc4gs60g5z4Vp2; Sat, 31 Jul 2021 00:21:29 +0000 (UTC) (envelope-from git@FreeBSD.org) Received: from gitrepo.freebsd.org (gitrepo.freebsd.org [IPv6:2610:1c1:1:6068::e6a:5]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (Client did not present a certificate) by mxrelay.nyi.freebsd.org (Postfix) with ESMTPS id 0703A6C31; Sat, 31 Jul 2021 00:21:29 +0000 (UTC) (envelope-from git@FreeBSD.org) Received: from gitrepo.freebsd.org ([127.0.1.44]) by gitrepo.freebsd.org (8.16.1/8.16.1) with ESMTP id 16V0LSKG052043; Sat, 31 Jul 2021 00:21:28 GMT (envelope-from git@gitrepo.freebsd.org) Received: (from git@localhost) by gitrepo.freebsd.org (8.16.1/8.16.1/Submit) id 16V0LSE2052042; Sat, 31 Jul 2021 00:21:28 GMT (envelope-from git) Date: Sat, 31 Jul 2021 00:21:28 GMT Message-Id: <202107310021.16V0LSE2052042@gitrepo.freebsd.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-branches@FreeBSD.org From: Warner Losh Subject: git: 644837397fa7 - stable/12 - nvme: Remove a wmb() that's not necessary. MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit X-Git-Committer: imp X-Git-Repository: src X-Git-Refname: refs/heads/stable/12 X-Git-Reftype: branch X-Git-Commit: 644837397fa7fbc6f5bdd7d885c6347045c18bf3 Auto-Submitted: auto-generated X-BeenThere: dev-commits-src-all@freebsd.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: Commit messages for all branches of the src repository List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sat, 31 Jul 2021 00:21:31 -0000 The branch stable/12 has been updated by imp: URL: https://cgit.FreeBSD.org/src/commit/?id=644837397fa7fbc6f5bdd7d885c6347045c18bf3 commit 644837397fa7fbc6f5bdd7d885c6347045c18bf3 Author: Warner Losh AuthorDate: 2020-12-04 21:34:48 +0000 Commit: Warner Losh CommitDate: 2021-07-31 00:02:52 +0000 nvme: Remove a wmb() that's not necessary. bus_dmamap_sync() ensures that memory that's prepared for PREWRITE can be DMA'd immediately after it returns. The details differ, but this mirrors atomic thread release semantics, at least for the buffers synced. For non-x86 platforms, bus_dmamap_sync() has the right syncing and fences. So in the past, wmb() had been omitted for them. For x86 platforms, the memory ordering is already strong enough to ensure DMA to the device sees the current contents. As such, we don't need the wmb() here. It translates to an sfence which is only needed for writes to regions that have the write combining attribute set or when some exotic opcodes are used. The nvme driver does neither of these. Since bus_dmamap_sync() includes atomic_thread_fence_rel, we can be assured any optimizer won't reorder the bus_dmamap_sync and the bus_space_write operations. The wmb() was a vestiage of the pre-busdma version initially committed to the tree. Reviewed by: kib@, gallatin@, chuck@, mav@ Differential Revision: https://reviews.freebsd.org/D27448 (cherry picked from commit 082905cad121bf6721606b6b9ba20a09bc6e56d0) --- sys/dev/nvme/nvme_qpair.c | 8 -------- 1 file changed, 8 deletions(-) diff --git a/sys/dev/nvme/nvme_qpair.c b/sys/dev/nvme/nvme_qpair.c index e43e8285e9bb..651eee121be1 100644 --- a/sys/dev/nvme/nvme_qpair.c +++ b/sys/dev/nvme/nvme_qpair.c @@ -987,14 +987,6 @@ nvme_qpair_submit_tracker(struct nvme_qpair *qpair, struct nvme_tracker *tr) bus_dmamap_sync(qpair->dma_tag, qpair->queuemem_map, BUS_DMASYNC_PREREAD | BUS_DMASYNC_PREWRITE); -#if !defined( __powerpc__) && !defined( __aarch64__) && !defined( __arm__) - /* - * powerpc's bus_dmamap_sync() already includes a heavyweight sync, but - * no other archs do. - */ - wmb(); -#endif - bus_space_write_4(qpair->ctrlr->bus_tag, qpair->ctrlr->bus_handle, qpair->sq_tdbl_off, qpair->sq_tail); qpair->num_cmds++;