On Thu, Dec 03, 2020 at 09:14:22AM -0800, Andy Lutomirski wrote:
>
>
> > On Dec 3, 2020, at 9:09 AM, Alexander Gordeev
> > wrote:
> >
> > On Mon, Nov 30, 2020 at 10:31:51AM -0800, Andy Lutomirski wrote:
> >> other arch folk: there's some background here:
>
> >
> >>
> >> power: Ridiculously
> On Dec 3, 2020, at 9:09 AM, Alexander Gordeev wrote:
>
> On Mon, Nov 30, 2020 at 10:31:51AM -0800, Andy Lutomirski wrote:
>> other arch folk: there's some background here:
>
>>
>> power: Ridiculously complicated, seems to vary by system and kernel config.
>>
>> So, Nick, your unconditio
On Mon, Nov 30, 2020 at 10:31:51AM -0800, Andy Lutomirski wrote:
> other arch folk: there's some background here:
>
> https://lkml.kernel.org/r/calcetrvxube8lfnn-qs+dzroqaiw+sfug1j047ybyv31sat...@mail.gmail.com
>
> On Sun, Nov 29, 2020 at 12:16 PM Andy Lutomirski wrote:
> >
> > On Sat, Nov 28, 2
> On Dec 1, 2020, at 7:47 PM, Nicholas Piggin wrote:
>
> Excerpts from Andy Lutomirski's message of December 1, 2020 4:31 am:
>> other arch folk: there's some background here:
>>
>> https://lkml.kernel.org/r/calcetrvxube8lfnn-qs+dzroqaiw+sfug1j047ybyv31sat...@mail.gmail.com
>>
>>> On Sun, Nov 29,
On Wed, Dec 02, 2020 at 06:38:12AM -0800, Andy Lutomirski wrote:
>
> > On Dec 2, 2020, at 6:20 AM, Peter Zijlstra wrote:
> >
> > On Sun, Nov 29, 2020 at 02:01:39AM +1000, Nicholas Piggin wrote:
> >> + * - A delayed freeing and RCU-like quiescing sequence based on
> >> + * mm s
> On Dec 2, 2020, at 6:20 AM, Peter Zijlstra wrote:
>
> On Sun, Nov 29, 2020 at 02:01:39AM +1000, Nicholas Piggin wrote:
>> + * - A delayed freeing and RCU-like quiescing sequence based on
>> + * mm switching to avoid IPIs completely.
>
> That one's interesting too. so basic
On Sun, Nov 29, 2020 at 02:01:39AM +1000, Nicholas Piggin wrote:
> + * - A delayed freeing and RCU-like quiescing sequence based on
> + * mm switching to avoid IPIs completely.
That one's interesting too. so basically you want to count switch_mm()
invocations on each CP
On Wed, Dec 02, 2020 at 12:17:31PM +0100, Peter Zijlstra wrote:
> So the obvious 'improvement' here would be something like:
>
> for_each_online_cpu(cpu) {
> p = rcu_dereference(cpu_rq(cpu)->curr;
> if (p->active_mm != mm)
> continue;
>
On Sun, Nov 29, 2020 at 02:01:39AM +1000, Nicholas Piggin wrote:
> +static void shoot_lazy_tlbs(struct mm_struct *mm)
> +{
> + if (IS_ENABLED(CONFIG_MMU_LAZY_TLB_SHOOTDOWN)) {
> + /*
> + * IPI overheads have not found to be expensive, but they could
> + * b
Excerpts from Andy Lutomirski's message of December 1, 2020 4:31 am:
> other arch folk: there's some background here:
>
> https://lkml.kernel.org/r/calcetrvxube8lfnn-qs+dzroqaiw+sfug1j047ybyv31sat...@mail.gmail.com
>
> On Sun, Nov 29, 2020 at 12:16 PM Andy Lutomirski wrote:
>>
>> On Sat, Nov 28,
Excerpts from Andy Lutomirski's message of November 29, 2020 1:54 pm:
> On Sat, Nov 28, 2020 at 8:02 AM Nicholas Piggin wrote:
>>
>> On big systems, the mm refcount can become highly contented when doing
>> a lot of context switching with threaded applications (particularly
>> switching between th
On Tue, Dec 01, 2020 at 01:50:38PM -0800, Andy Lutomirski wrote:
> On Tue, Dec 1, 2020 at 1:28 PM Will Deacon wrote:
> >
> > On Mon, Nov 30, 2020 at 10:31:51AM -0800, Andy Lutomirski wrote:
> > > other arch folk: there's some background here:
> > >
> > > https://lkml.kernel.org/r/calcetrvxube8lfnn
On Tue, Dec 1, 2020 at 1:28 PM Will Deacon wrote:
>
> On Mon, Nov 30, 2020 at 10:31:51AM -0800, Andy Lutomirski wrote:
> > other arch folk: there's some background here:
> >
> > https://lkml.kernel.org/r/calcetrvxube8lfnn-qs+dzroqaiw+sfug1j047ybyv31sat...@mail.gmail.com
> >
> > On Sun, Nov 29, 202
On Mon, Nov 30, 2020 at 10:31:51AM -0800, Andy Lutomirski wrote:
> other arch folk: there's some background here:
>
> https://lkml.kernel.org/r/calcetrvxube8lfnn-qs+dzroqaiw+sfug1j047ybyv31sat...@mail.gmail.com
>
> On Sun, Nov 29, 2020 at 12:16 PM Andy Lutomirski wrote:
> >
> > On Sat, Nov 28, 2
other arch folk: there's some background here:
https://lkml.kernel.org/r/calcetrvxube8lfnn-qs+dzroqaiw+sfug1j047ybyv31sat...@mail.gmail.com
On Sun, Nov 29, 2020 at 12:16 PM Andy Lutomirski wrote:
>
> On Sat, Nov 28, 2020 at 7:54 PM Andy Lutomirski wrote:
> >
> > On Sat, Nov 28, 2020 at 8:02 AM
On Mon, Nov 30, 2020 at 10:30:00AM +0100, Peter Zijlstra wrote:
> On Sat, Nov 28, 2020 at 07:54:57PM -0800, Andy Lutomirski wrote:
> > This means that mm_cpumask operations won't need to be full barriers
> > forever, and we might not want to take the implied full barriers in
> > set_bit() and clear
On Sat, Nov 28, 2020 at 07:54:57PM -0800, Andy Lutomirski wrote:
> This means that mm_cpumask operations won't need to be full barriers
> forever, and we might not want to take the implied full barriers in
> set_bit() and clear_bit() for granted.
There is no implied full barrier for those ops.
On Sat, Nov 28, 2020 at 07:54:57PM -0800, Andy Lutomirski wrote:
> Version (b) seems fairly straightforward to implement -- add RCU
> protection and a atomic_t special_ref_cleared (initially 0) to struct
> mm_struct itself. After anyone clears a bit to mm_cpumask (which is
> already a barrier),
N
On Sun, Nov 29, 2020 at 12:16:26PM -0800, Andy Lutomirski wrote:
> On Sat, Nov 28, 2020 at 7:54 PM Andy Lutomirski wrote:
> >
> > On Sat, Nov 28, 2020 at 8:02 AM Nicholas Piggin wrote:
> > >
> > > On big systems, the mm refcount can become highly contented when doing
> > > a lot of context switch
On Sat, Nov 28, 2020 at 7:54 PM Andy Lutomirski wrote:
>
> On Sat, Nov 28, 2020 at 8:02 AM Nicholas Piggin wrote:
> >
> > On big systems, the mm refcount can become highly contented when doing
> > a lot of context switching with threaded applications (particularly
> > switching between the idle t
On Sat, Nov 28, 2020 at 8:02 AM Nicholas Piggin wrote:
>
> On big systems, the mm refcount can become highly contented when doing
> a lot of context switching with threaded applications (particularly
> switching between the idle thread and an application thread).
>
> Abandoning lazy tlb slows swit
On big systems, the mm refcount can become highly contented when doing
a lot of context switching with threaded applications (particularly
switching between the idle thread and an application thread).
Abandoning lazy tlb slows switching down quite a bit in the important
user->idle->user cases, so
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