From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 511B8C432C0 for ; Wed, 27 Nov 2019 18:42:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 33165207DD for ; Wed, 27 Nov 2019 18:42:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727050AbfK0Smi (ORCPT ); Wed, 27 Nov 2019 13:42:38 -0500 Received: from mga17.intel.com ([192.55.52.151]:43591 "EHLO mga17.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726593AbfK0Smi (ORCPT ); Wed, 27 Nov 2019 13:42:38 -0500 X-Amp-Result: UNKNOWN X-Amp-Original-Verdict: FILE UNKNOWN X-Amp-File-Uploaded: False Received: from orsmga007.jf.intel.com ([10.7.209.58]) by fmsmga107.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 27 Nov 2019 10:42:37 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.69,250,1571727600"; d="scan'208";a="199277686" Received: from sjchrist-coffee.jf.intel.com (HELO linux.intel.com) ([10.54.74.41]) by orsmga007.jf.intel.com with ESMTP; 27 Nov 2019 10:42:37 -0800 Date: Wed, 27 Nov 2019 10:42:37 -0800 From: Sean Christopherson To: Ben Gardon Cc: kvm@vger.kernel.org, Paolo Bonzini , Peter Feiner , Peter Shier , Junaid Shahid , Jim Mattson Subject: Re: [RFC PATCH 05/28] sched: Add cond_resched_rwlock Message-ID: <20191127184237.GE22227@linux.intel.com> References: <20190926231824.149014-1-bgardon@google.com> <20190926231824.149014-6-bgardon@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190926231824.149014-6-bgardon@google.com> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Thu, Sep 26, 2019 at 04:18:01PM -0700, Ben Gardon wrote: > Rescheduling while holding a spin lock is essential for keeping long > running kernel operations running smoothly. Add the facility to > cond_resched read/write spin locks. > > RFC_NOTE: The current implementation of this patch set uses a read/write > lock to replace the existing MMU spin lock. See the next patch in this > series for more on why a read/write lock was chosen, and possible > alternatives. This definitely needs to be run by the sched/locking folks sooner rather than later. > Signed-off-by: Ben Gardon > --- > include/linux/sched.h | 11 +++++++++++ > kernel/sched/core.c | 23 +++++++++++++++++++++++ > 2 files changed, 34 insertions(+) > > diff --git a/include/linux/sched.h b/include/linux/sched.h > index 70db597d6fd4f..4d1fd96693d9b 100644 > --- a/include/linux/sched.h > +++ b/include/linux/sched.h > @@ -1767,12 +1767,23 @@ static inline int _cond_resched(void) { return 0; } > }) > > extern int __cond_resched_lock(spinlock_t *lock); > +extern int __cond_resched_rwlock(rwlock_t *lock, bool write_lock); > > #define cond_resched_lock(lock) ({ \ > ___might_sleep(__FILE__, __LINE__, PREEMPT_LOCK_OFFSET);\ > __cond_resched_lock(lock); \ > }) > > +#define cond_resched_rwlock_read(lock) ({ \ > + __might_sleep(__FILE__, __LINE__, PREEMPT_LOCK_OFFSET); \ > + __cond_resched_rwlock(lock, false); \ > +}) > + > +#define cond_resched_rwlock_write(lock) ({ \ > + __might_sleep(__FILE__, __LINE__, PREEMPT_LOCK_OFFSET); \ > + __cond_resched_rwlock(lock, true); \ > +}) > + > static inline void cond_resched_rcu(void) > { > #if defined(CONFIG_DEBUG_ATOMIC_SLEEP) || !defined(CONFIG_PREEMPT_RCU) > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index f9a1346a5fa95..ba7ed4bed5036 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -5663,6 +5663,29 @@ int __cond_resched_lock(spinlock_t *lock) > } > EXPORT_SYMBOL(__cond_resched_lock); > > +int __cond_resched_rwlock(rwlock_t *lock, bool write_lock) > +{ > + int ret = 0; > + > + lockdep_assert_held(lock); > + if (should_resched(PREEMPT_LOCK_OFFSET)) { > + if (write_lock) { The existing __cond_resched_lock() checks for resched *or* lock contention. Is lock contention not something that needs (or can't?) be considered? > + write_unlock(lock); > + preempt_schedule_common(); > + write_lock(lock); > + } else { > + read_unlock(lock); > + preempt_schedule_common(); > + read_lock(lock); > + } > + > + ret = 1; > + } > + > + return ret; > +} > +EXPORT_SYMBOL(__cond_resched_rwlock); > + > /** > * yield - yield the current processor to other threads. > * > -- > 2.23.0.444.g18eeb5a265-goog >