From mboxrd@z Thu Jan 1 00:00:00 1970 From: Oleg Nesterov Subject: Re: TIF_NOHZ can escape nonhz mask? (Was: [PATCH v3 6/8] x86: Split syscall_trace_enter into two phases) Date: Thu, 31 Jul 2014 21:05:18 +0200 Message-ID: <20140731190518.GA21938@redhat.com> References: <20140728192209.GA26017@localhost.localdomain> <20140729175414.GA3289@redhat.com> <20140730163516.GC18158@localhost.localdomain> <20140730174630.GA30862@redhat.com> <20140731003034.GA32078@localhost.localdomain> <20140731160353.GA14772@redhat.com> <20140731171329.GD7842@localhost.localdomain> <20140731181230.GA18695@redhat.com> <20140731184729.GA12296@localhost.localdomain> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-mips-bounce@linux-mips.org Errors-to: linux-mips-bounce@linux-mips.org List-help: List-unsubscribe: List-software: Ecartis version 1.0.0 List-subscribe: List-owner: List-post: List-archive: To: Frederic Weisbecker Cc: Andy Lutomirski , "Paul E. McKenney" , LKML , Kees Cook , Will Drewry , the arch/x86 maintainers , "" , Linux MIPS Mailing List , "linux-arch@vger.kernel.org" , LSM List , Alexei Starovoitov , "H. Peter Anvin" List-Id: linux-arch.vger.kernel.org On 07/31, Frederic Weisbecker wrote: > > 2014-07-31 20:47 GMT+02:00 Frederic Weisbecker : > > On Thu, Jul 31, 2014 at 08:12:30PM +0200, Oleg Nesterov wrote: > >> On 07/31, Frederic Weisbecker wrote: > > No, because preempt_schedule_irq() does the ctx_state save and restore with > > exception_enter/exception_exit. > > Similar thing happens with schedule_user(). > > preempt_schedule_irq() handles kernel preemption and schedule_user() > the user preemption. On both cases we save and restore the context > tracking state. > > This might be the missing piece you were missing :) YYYYYEEEEESSSS, thanks!! And in fact I was going to suggest to add this logic into preempt schedule paths to improve the situation if we can't make TIF_NOHZ per-cpu. But Frederic, perhaps I'll return here tomorrow with another question, it is too late for me now ;) Thanks! Oleg. From mboxrd@z Thu Jan 1 00:00:00 1970 From: oleg@redhat.com (Oleg Nesterov) Date: Thu, 31 Jul 2014 21:05:18 +0200 Subject: TIF_NOHZ can escape nonhz mask? (Was: [PATCH v3 6/8] x86: Split syscall_trace_enter into two phases) In-Reply-To: References: <20140728192209.GA26017@localhost.localdomain> <20140729175414.GA3289@redhat.com> <20140730163516.GC18158@localhost.localdomain> <20140730174630.GA30862@redhat.com> <20140731003034.GA32078@localhost.localdomain> <20140731160353.GA14772@redhat.com> <20140731171329.GD7842@localhost.localdomain> <20140731181230.GA18695@redhat.com> <20140731184729.GA12296@localhost.localdomain> Message-ID: <20140731190518.GA21938@redhat.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On 07/31, Frederic Weisbecker wrote: > > 2014-07-31 20:47 GMT+02:00 Frederic Weisbecker : > > On Thu, Jul 31, 2014 at 08:12:30PM +0200, Oleg Nesterov wrote: > >> On 07/31, Frederic Weisbecker wrote: > > No, because preempt_schedule_irq() does the ctx_state save and restore with > > exception_enter/exception_exit. > > Similar thing happens with schedule_user(). > > preempt_schedule_irq() handles kernel preemption and schedule_user() > the user preemption. On both cases we save and restore the context > tracking state. > > This might be the missing piece you were missing :) YYYYYEEEEESSSS, thanks!! And in fact I was going to suggest to add this logic into preempt schedule paths to improve the situation if we can't make TIF_NOHZ per-cpu. But Frederic, perhaps I'll return here tomorrow with another question, it is too late for me now ;) Thanks! Oleg.