linux-kernel - Re: [PATCH] hrtimer: Replace cpu_base->active_bases with a direct check of the active list

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <alpine.DEB.2.11.1504130953320.3845@nanos>
Date:	Mon, 13 Apr 2015 09:53:55 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Preeti U Murthy <preeti@...ux.vnet.ibm.com>
cc:	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	Ingo Molnar <mingo@...hat.com>, linaro-kernel@...ts.linaro.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] hrtimer: Replace cpu_base->active_bases with a direct
 check of the active list

On Mon, 13 Apr 2015, Preeti U Murthy wrote:
> On 04/09/2015 02:48 PM, Thomas Gleixner wrote:
> > On Thu, 9 Apr 2015, Peter Zijlstra wrote:
> >> On Thu, Apr 09, 2015 at 09:20:39AM +0200, Ingo Molnar wrote:
> >>> if at least one base is active (on my fairly standard system all cpus 
> >>> have at least one active hrtimer base all the time - and many cpus 
> >>> have two bases active), then we run hrtimer_get_softirq_time(), which 
> >>> dirties the cachelines of all 4 clock bases:
> >>>
> >>>         base->clock_base[HRTIMER_BASE_REALTIME].softirq_time = xtim;
> >>>         base->clock_base[HRTIMER_BASE_MONOTONIC].softirq_time = mono;
> >>>         base->clock_base[HRTIMER_BASE_BOOTTIME].softirq_time = boot;
> >>>         base->clock_base[HRTIMER_BASE_TAI].softirq_time = tai;
> >>>
> >>> so in practice we not only touch every cacheline in every timer 
> >>> interrupt, but we _dirty_ them, even the inactive ones.
> >>>
> >>
> >> Urgh we should really _really_ kill that entire softirq mess.
> > 
> > That's the !highres part. We cannot kill that one unless we remove all
> > support for machines which do not provide hardware for highres
> > support.
> > 
> > Now the softirq_time thing is an optimization which we added back in
> > the days when hrtimer went into the tree and Roman complained about
> > the base->get_time() invocation being overkill.
> > 
> > The reasoning behing this was that low resolution systems do not need
> > accurate time for the expiry and the forwarding because everything
> > happens tick aligned.
> > 
> > So for !HIGHRES we have:
> > 
> > static inline ktime_t hrtimer_cb_get_time(struct hrtimer *timer)
> > {
> > 	return timer->base->softirq_time;
> > }
> 
> Why is this called softirq_time when the hrtimer is being serviced in
> the hard irq context ?

For historical reasons.

Thanks,

	tglx
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/