From patchwork Mon Jul 22 06:19:15 2013 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Raghavendra K T X-Patchwork-Id: 2831058 Return-Path: X-Original-To: patchwork-kvm@patchwork.kernel.org Delivered-To: patchwork-parsemail@patchwork2.web.kernel.org Received: from mail.kernel.org (mail.kernel.org [198.145.19.201]) by patchwork2.web.kernel.org (Postfix) with ESMTP id AE6B0C0319 for ; Mon, 22 Jul 2013 06:12:20 +0000 (UTC) Received: from mail.kernel.org (localhost [127.0.0.1]) by mail.kernel.org (Postfix) with ESMTP id B521D2016D for ; Mon, 22 Jul 2013 06:12:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id BDAAA2015D for ; Mon, 22 Jul 2013 06:12:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756456Ab3GVGL7 (ORCPT ); Mon, 22 Jul 2013 02:11:59 -0400 Received: from e23smtp09.au.ibm.com ([202.81.31.142]:47921 "EHLO e23smtp09.au.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756271Ab3GVGL4 (ORCPT ); Mon, 22 Jul 2013 02:11:56 -0400 Received: from /spool/local by e23smtp09.au.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! 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Violators will be prosecuted; Tue, 23 Jul 2013 03:07:12 +1000 Received: from d23relay04.au.ibm.com (d23relay04.au.ibm.com [9.190.234.120]) by d23dlp01.au.ibm.com (Postfix) with ESMTP id 2D1EC2CE8053; Mon, 22 Jul 2013 16:11:51 +1000 (EST) Received: from d23av03.au.ibm.com (d23av03.au.ibm.com [9.190.234.97]) by d23relay04.au.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id r6M5uTBB8061242; Mon, 22 Jul 2013 15:56:29 +1000 Received: from d23av03.au.ibm.com (loopback [127.0.0.1]) by d23av03.au.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id r6M6Bli3029474; Mon, 22 Jul 2013 16:11:50 +1000 Received: from [9.124.158.46] ([9.124.158.46]) by d23av03.au.ibm.com (8.14.4/8.13.1/NCO v10.0 AVin) with ESMTP id r6M6BfAK029293; Mon, 22 Jul 2013 16:11:42 +1000 From: Raghavendra K T To: , , , , , , Cc: linux-doc@vger.kernel.org, , Raghavendra K T , , , , , , , , , , , , , , , , , , , Date: Mon, 22 Jul 2013 11:49:15 +0530 Message-Id: <20130722061915.24737.73186.sendpatchset@codeblue> In-Reply-To: <20130722061631.24737.75508.sendpatchset@codeblue> References: <20130722061631.24737.75508.sendpatchset@codeblue> Subject: [PATCH RFC V11 11/18] xen/pvticketlock: Allow interrupts to be enabled while blocking X-Content-Scanned: Fidelis XPS MAILER x-cbid: 13072217-3568-0000-0000-000003F6B4BE Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org X-Spam-Status: No, score=-8.3 required=5.0 tests=BAYES_00, RCVD_IN_DNSWL_HI, RP_MATCHES_RCVD, UNPARSEABLE_RELAY autolearn=unavailable version=3.3.1 X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on mail.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP xen/pvticketlock: Allow interrupts to be enabled while blocking From: Jeremy Fitzhardinge If interrupts were enabled when taking the spinlock, we can leave them enabled while blocking to get the lock. If we can enable interrupts while waiting for the lock to become available, and we take an interrupt before entering the poll, and the handler takes a spinlock which ends up going into the slow state (invalidating the per-cpu "lock" and "want" values), then when the interrupt handler returns the event channel will remain pending so the poll will return immediately, causing it to return out to the main spinlock loop. Signed-off-by: Jeremy Fitzhardinge Reviewed-by: Konrad Rzeszutek Wilk Signed-off-by: Raghavendra K T --- arch/x86/xen/spinlock.c | 46 ++++++++++++++++++++++++++++++++++++++++------ 1 file changed, 40 insertions(+), 6 deletions(-) -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html diff --git a/arch/x86/xen/spinlock.c b/arch/x86/xen/spinlock.c index dff5841..44d06f3 100644 --- a/arch/x86/xen/spinlock.c +++ b/arch/x86/xen/spinlock.c @@ -142,7 +142,20 @@ static void xen_lock_spinning(struct arch_spinlock *lock, __ticket_t want) * partially setup state. */ local_irq_save(flags); - + /* + * We don't really care if we're overwriting some other + * (lock,want) pair, as that would mean that we're currently + * in an interrupt context, and the outer context had + * interrupts enabled. That has already kicked the VCPU out + * of xen_poll_irq(), so it will just return spuriously and + * retry with newly setup (lock,want). + * + * The ordering protocol on this is that the "lock" pointer + * may only be set non-NULL if the "want" ticket is correct. + * If we're updating "want", we must first clear "lock". + */ + w->lock = NULL; + smp_wmb(); w->want = want; smp_wmb(); w->lock = lock; @@ -157,24 +170,43 @@ static void xen_lock_spinning(struct arch_spinlock *lock, __ticket_t want) /* Only check lock once pending cleared */ barrier(); - /* Mark entry to slowpath before doing the pickup test to make - sure we don't deadlock with an unlocker. */ + /* + * Mark entry to slowpath before doing the pickup test to make + * sure we don't deadlock with an unlocker. + */ __ticket_enter_slowpath(lock); - /* check again make sure it didn't become free while - we weren't looking */ + /* + * check again make sure it didn't become free while + * we weren't looking + */ if (ACCESS_ONCE(lock->tickets.head) == want) { add_stats(TAKEN_SLOW_PICKUP, 1); goto out; } + + /* Allow interrupts while blocked */ + local_irq_restore(flags); + + /* + * If an interrupt happens here, it will leave the wakeup irq + * pending, which will cause xen_poll_irq() to return + * immediately. + */ + /* Block until irq becomes pending (or perhaps a spurious wakeup) */ xen_poll_irq(irq); add_stats(TAKEN_SLOW_SPURIOUS, !xen_test_irq_pending(irq)); + + local_irq_save(flags); + kstat_incr_irqs_this_cpu(irq, irq_to_desc(irq)); out: cpumask_clear_cpu(cpu, &waiting_cpus); w->lock = NULL; + local_irq_restore(flags); + spin_time_accum_blocked(start); } PV_CALLEE_SAVE_REGS_THUNK(xen_lock_spinning); @@ -188,7 +220,9 @@ static void xen_unlock_kick(struct arch_spinlock *lock, __ticket_t next) for_each_cpu(cpu, &waiting_cpus) { const struct xen_lock_waiting *w = &per_cpu(lock_waiting, cpu); - if (w->lock == lock && w->want == next) { + /* Make sure we read lock before want */ + if (ACCESS_ONCE(w->lock) == lock && + ACCESS_ONCE(w->want) == next) { add_stats(RELEASED_SLOW_KICKED, 1); xen_send_IPI_one(cpu, XEN_SPIN_UNLOCK_VECTOR); break;