From patchwork Wed Aug 16 11:22:08 2017 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Andrew Cooper X-Patchwork-Id: 9903493 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id 908FB6038C for ; Wed, 16 Aug 2017 11:24:25 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 8330B27CEA for ; Wed, 16 Aug 2017 11:24:25 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 782B328769; Wed, 16 Aug 2017 11:24:25 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-4.2 required=2.0 tests=BAYES_00, RCVD_IN_DNSWL_MED autolearn=ham version=3.3.1 Received: from lists.xenproject.org (lists.xenproject.org [192.237.175.120]) (using TLSv1.2 with cipher AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.wl.linuxfoundation.org (Postfix) with ESMTPS id 085D727CEA for ; Wed, 16 Aug 2017 11:24:25 +0000 (UTC) Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.84_2) (envelope-from ) id 1dhwOw-0006Bv-3Z; Wed, 16 Aug 2017 11:22:18 +0000 Received: from mail6.bemta6.messagelabs.com ([193.109.254.103]) by lists.xenproject.org with esmtp (Exim 4.84_2) (envelope-from ) id 1dhwOu-0006Aj-Ej for xen-devel@lists.xen.org; Wed, 16 Aug 2017 11:22:16 +0000 Received: from [193.109.254.147] by server-6.bemta-6.messagelabs.com id EA/DF-03937-7EA24995; Wed, 16 Aug 2017 11:22:15 +0000 X-Brightmail-Tracker: H4sIAAAAAAAAA+NgFupnkeJIrShJLcpLzFFi42JxWrrBXve51pR Igzt7pSyWfFzM4sDocXT3b6YAxijWzLyk/IoE1ozPu/eyFfzTqGjuvsrWwNih2MXIySEh4C9x 8vxMFhCbTUBfYveLT0wgtoiAusTpjousXYwcHMwCfhKHHviChIUFrCQWtWxhAgmzCKhKLL/hB BLmFfCUuHxiDgvERDmJ88d/MoPYnAJeEhf27ACbKARUc2vHPlYIW03iWv8ldoheQYmTM5+A9T ILSEgcfPGCeQIj7ywkqVlIUgsYmVYxahSnFpWlFukaGeolFWWmZ5TkJmbm6BoamOnlphYXJ6a n5iQmFesl5+duYgQGDgMQ7GD8syzgEKMkB5OSKO+is5MihfiS8lMqMxKLM+KLSnNSiw8xynBw KEnw1mpOiRQSLEpNT61Iy8wBhjBMWoKDR0mE9xFImre4IDG3ODMdInWKUZfj1YT/35iEWPLy8 1KlxHm9QYoEQIoySvPgRsDi6RKjrJQwLyPQUUI8BalFuZklqPKvGMU5GJWEeTeBTOHJzCuB2/ QK6AgmoCOutE8COaIkESEl1cC49otuuYqo1dr1+U+1LxzcpXPmm9nNmqJdzxz4czWF1jGzpRj nWt5wuXToieSJVbYCt5k/HNwde+ykmsuyH+cTgj/zTnu+RHTu/K5jhUzqR6XK+gL2MhzXlitM Da91epbdVhGg+GRW6pHziyJEStqvljJtWa+7pkoz+Gn+619n/zVY/lqktjBAiaU4I9FQi7moO BEArrYsuKICAAA= X-Env-Sender: prvs=3941fdc67=Andrew.Cooper3@citrix.com X-Msg-Ref: server-4.tower-27.messagelabs.com!1502882533!111246128!2 X-Originating-IP: [66.165.176.63] X-SpamReason: No, hits=0.0 required=7.0 tests=sa_preprocessor: VHJ1c3RlZCBJUDogNjYuMTY1LjE3Ni42MyA9PiAzMDYwNDg=\n, received_headers: No Received headers X-StarScan-Received: X-StarScan-Version: 9.4.45; banners=-,-,- X-VirusChecked: Checked Received: (qmail 5820 invoked from network); 16 Aug 2017 11:22:15 -0000 Received: from smtp02.citrix.com (HELO SMTP02.CITRIX.COM) (66.165.176.63) by server-4.tower-27.messagelabs.com with RC4-SHA encrypted SMTP; 16 Aug 2017 11:22:15 -0000 X-IronPort-AV: E=Sophos;i="5.41,382,1498521600"; d="scan'208";a="443987610" From: Andrew Cooper To: Xen-devel Date: Wed, 16 Aug 2017 12:22:08 +0100 Message-ID: <1502882530-31700-3-git-send-email-andrew.cooper3@citrix.com> X-Mailer: git-send-email 2.1.4 In-Reply-To: <1502882530-31700-1-git-send-email-andrew.cooper3@citrix.com> References: <1502882530-31700-1-git-send-email-andrew.cooper3@citrix.com> MIME-Version: 1.0 Cc: Andrew Cooper , Jan Beulich Subject: [Xen-devel] [PATCH v2 2/4] xen/x86: Drop unnecessary barriers X-BeenThere: xen-devel@lists.xen.org X-Mailman-Version: 2.1.18 Precedence: list List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Errors-To: xen-devel-bounces@lists.xen.org Sender: "Xen-devel" X-Virus-Scanned: ClamAV using ClamSMTP x86's current implementation of wmb() is a compiler barrier. As a result, the only change in this patch is to remove an mfence instruction from cpuidle_disable_deep_cstate(). None of these barriers serve any purpose. Most aren't aren't synchronising with any remote cpus, where as the mcetelem barriers are redundant with spin_unlock(), which already has full read/write barrier semantics. Signed-off-by: Andrew Cooper Acked-by: Jan Beulich --- CC: Jan Beulich v2: * s/erronious/unnecessary/ * Drop more unnecessary barriers --- xen/arch/x86/acpi/cpu_idle.c | 2 -- xen/arch/x86/cpu/mcheck/mce.c | 3 --- xen/arch/x86/cpu/mcheck/mctelem.c | 3 --- xen/arch/x86/crash.c | 3 --- xen/arch/x86/mm/shadow/multi.c | 1 - xen/arch/x86/smpboot.c | 2 -- xen/drivers/passthrough/amd/iommu_init.c | 2 -- 7 files changed, 16 deletions(-) diff --git a/xen/arch/x86/acpi/cpu_idle.c b/xen/arch/x86/acpi/cpu_idle.c index 482b8a7..5879ad6 100644 --- a/xen/arch/x86/acpi/cpu_idle.c +++ b/xen/arch/x86/acpi/cpu_idle.c @@ -1331,8 +1331,6 @@ void cpuidle_disable_deep_cstate(void) max_cstate = 1; } - mb(); - hpet_disable_legacy_broadcast(); } diff --git a/xen/arch/x86/cpu/mcheck/mce.c b/xen/arch/x86/cpu/mcheck/mce.c index 30525dd..aa6e556 100644 --- a/xen/arch/x86/cpu/mcheck/mce.c +++ b/xen/arch/x86/cpu/mcheck/mce.c @@ -86,7 +86,6 @@ static x86_mce_vector_t _machine_check_vector = unexpected_machine_check; void x86_mce_vector_register(x86_mce_vector_t hdlr) { _machine_check_vector = hdlr; - wmb(); } /* Call the installed machine check handler for this CPU setup. */ @@ -369,8 +368,6 @@ mcheck_mca_logout(enum mca_source who, struct mca_banks *bankmask, mcabank_clear(i); else if ( who == MCA_MCE_SCAN && need_clear) mcabanks_set(i, clear_bank); - - wmb(); } if (mig && errcnt > 0) { diff --git a/xen/arch/x86/cpu/mcheck/mctelem.c b/xen/arch/x86/cpu/mcheck/mctelem.c index b144a66..1731514 100644 --- a/xen/arch/x86/cpu/mcheck/mctelem.c +++ b/xen/arch/x86/cpu/mcheck/mctelem.c @@ -520,7 +520,6 @@ mctelem_cookie_t mctelem_consume_oldest_begin(mctelem_class_t which) } mctelem_processing_hold(tep); - wmb(); spin_unlock(&processing_lock); return MCTE2COOKIE(tep); } @@ -531,7 +530,6 @@ void mctelem_consume_oldest_end(mctelem_cookie_t cookie) spin_lock(&processing_lock); mctelem_processing_release(tep); - wmb(); spin_unlock(&processing_lock); } @@ -547,6 +545,5 @@ void mctelem_ack(mctelem_class_t which, mctelem_cookie_t cookie) spin_lock(&processing_lock); if (tep == mctctl.mctc_processing_head[target]) mctelem_processing_release(tep); - wmb(); spin_unlock(&processing_lock); } diff --git a/xen/arch/x86/crash.c b/xen/arch/x86/crash.c index 82535c4..8d74258 100644 --- a/xen/arch/x86/crash.c +++ b/xen/arch/x86/crash.c @@ -146,9 +146,6 @@ static void nmi_shootdown_cpus(void) write_atomic((unsigned long *)__va(__pa(&exception_table[TRAP_nmi])), (unsigned long)&do_nmi_crash); - /* Ensure the new callback function is set before sending out the NMI. */ - wmb(); - smp_send_nmi_allbutself(); msecs = 1000; /* Wait at most a second for the other cpus to stop */ diff --git a/xen/arch/x86/mm/shadow/multi.c b/xen/arch/x86/mm/shadow/multi.c index c9c2252..1e3dfaf 100644 --- a/xen/arch/x86/mm/shadow/multi.c +++ b/xen/arch/x86/mm/shadow/multi.c @@ -3112,7 +3112,6 @@ static int sh_page_fault(struct vcpu *v, * will make sure no inconsistent mapping being translated into * shadow page table. */ version = atomic_read(&d->arch.paging.shadow.gtable_dirty_version); - rmb(); walk_ok = sh_walk_guest_tables(v, va, &gw, error_code); #if (SHADOW_OPTIMIZATIONS & SHOPT_OUT_OF_SYNC) diff --git a/xen/arch/x86/smpboot.c b/xen/arch/x86/smpboot.c index 8d91f6c..5b094b4 100644 --- a/xen/arch/x86/smpboot.c +++ b/xen/arch/x86/smpboot.c @@ -355,7 +355,6 @@ void start_secondary(void *unused) spin_debug_enable(); set_cpu_sibling_map(cpu); notify_cpu_starting(cpu); - wmb(); /* * We need to hold vector_lock so there the set of online cpus @@ -371,7 +370,6 @@ void start_secondary(void *unused) local_irq_enable(); mtrr_ap_init(); - wmb(); startup_cpu_idle_loop(); } diff --git a/xen/drivers/passthrough/amd/iommu_init.c b/xen/drivers/passthrough/amd/iommu_init.c index a459e99..d5b6049 100644 --- a/xen/drivers/passthrough/amd/iommu_init.c +++ b/xen/drivers/passthrough/amd/iommu_init.c @@ -558,7 +558,6 @@ static void parse_event_log_entry(struct amd_iommu *iommu, u32 entry[]) return; } udelay(1); - rmb(); code = get_field_from_reg_u32(entry[1], IOMMU_EVENT_CODE_MASK, IOMMU_EVENT_CODE_SHIFT); } @@ -663,7 +662,6 @@ void parse_ppr_log_entry(struct amd_iommu *iommu, u32 entry[]) return; } udelay(1); - rmb(); code = get_field_from_reg_u32(entry[1], IOMMU_PPR_LOG_CODE_MASK, IOMMU_PPR_LOG_CODE_SHIFT); }