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From: Will Deacon <will@kernel.org>
To: Guo Ren <guoren@kernel.org>
Cc: Julien Grall <julien.grall@arm.com>,
	aou@eecs.berkeley.edu, Marc Zyngier <marc.zyngier@arm.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will.deacon@arm.com>,
	linux-kernel@vger.kernel.org, rppt@linux.ibm.com,
	hch@infradead.org, Atish Patra <Atish.Patra@wdc.com>,
	Anup Patel <anup.Patel@wdc.com>,
	gary@garyguo.net, Palmer Dabbelt <palmer@sifive.com>,
	paul.walmsley@sifive.com, linux-riscv@lists.infradead.org,
	kvmarm@lists.cs.columbia.edu,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH RFC 11/14] arm64: Move the ASID allocator code in a separate file
Date: Mon, 24 Jun 2019 11:22:10 +0100
Message-ID: <20190624102209.ngwtosgr5fvp3ler@willie-the-truck> (raw)
In-Reply-To: <CAJF2gTTVUToRkRtxTmtWDotMGXy5YQCpL1h_2neTBuN3e6oz1w@mail.gmail.com>

On Mon, Jun 24, 2019 at 12:35:35AM +0800, Guo Ren wrote:
> On Fri, Jun 21, 2019 at 10:16 PM Catalin Marinas
> <catalin.marinas@arm.com> wrote:
> >
> > On Wed, Jun 19, 2019 at 07:51:03PM +0800, Guo Ren wrote:
> > > On Wed, Jun 19, 2019 at 4:54 PM Julien Grall <julien.grall@arm.com> wrote:
> > > > On 6/19/19 9:07 AM, Guo Ren wrote:
> > > > > Move arm asid allocator code in a generic one is a agood idea, I've
> > > > > made a patchset for C-SKY and test is on processing, See:
> > > > > https://lore.kernel.org/linux-csky/1560930553-26502-1-git-send-email-guoren@kernel.org/
> > > > >
> > > > > If you plan to seperate it into generic one, I could co-work with you.
> > > >
> > > > Was the ASID allocator work out of box on C-Sky?
> > >
> > > Almost done, but one question:
> > > arm64 remove the code in switch_mm:
> > >   cpumask_clear_cpu(cpu, mm_cpumask(prev));
> > >   cpumask_set_cpu(cpu, mm_cpumask(next));
> > >
> > > Why? Although arm64 cache operations could affect all harts with CTC
> > > method of interconnect, I think we should keep these code for
> > > primitive integrity in linux. Because cpu_bitmap is in mm_struct
> > > instead of mm->context.
> >
> > We didn't have a use for this in the arm64 code, so no point in
> > maintaining the mm_cpumask. On some arm32 systems (ARMv6) with no
> > hardware broadcast of some TLB/cache operations, we use it to track
> > where the task has run to issue IPI for TLB invalidation or some
> > deferred I-cache invalidation.
> The operation of set/clear mm_cpumask was removed in arm64 compared to
> arm32. It seems no side effect on current arm64 system, but from
> software meaning it's wrong.
> I think we should keep mm_cpumask just like arm32.

It was a while ago now, but I remember the atomic update of the mm_cpumask
being quite expensive when I was profiling this stuff, so I removed it
because we don't need it for arm64 (at least, it doesn't allow us to
optimise our shootdowns in practice).

I still think this is over-engineered for what you want on c-sky and making
this code generic is a mistake.

Will
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Thread overview: 56+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-03-21 16:36 [PATCH RFC 00/14] kvm/arm: Align the VMID allocation with the arm64 ASID one Julien Grall
2019-03-21 16:36 ` [PATCH RFC 01/14] arm64/mm: Introduce asid_info structure and move asid_generation/asid_map to it Julien Grall
2019-03-21 17:03   ` Suzuki K Poulose
2019-03-21 17:27     ` Julien Grall
2019-03-21 16:36 ` [PATCH RFC 02/14] arm64/mm: Move active_asids and reserved_asids to asid_info Julien Grall
2019-03-21 16:36 ` [PATCH RFC 03/14] arm64/mm: Move bits " Julien Grall
2019-03-21 16:36 ` [PATCH RFC 04/14] arm64/mm: Move the variable lock and tlb_flush_pending " Julien Grall
2019-03-21 16:36 ` [PATCH RFC 05/14] arm64/mm: Remove dependency on MM in new_context Julien Grall
2019-03-21 16:36 ` [PATCH RFC 06/14] arm64/mm: Store the number of asid allocated per context Julien Grall
2019-03-21 16:36 ` [PATCH RFC 07/14] arm64/mm: Introduce NUM_ASIDS Julien Grall
2019-03-21 16:36 ` [PATCH RFC 08/14] arm64/mm: Split asid_inits in 2 parts Julien Grall
2019-03-21 16:36 ` [PATCH RFC 09/14] arm64/mm: Split the function check_and_switch_context in 3 parts Julien Grall
2019-03-21 16:36 ` [PATCH RFC 10/14] arm64/mm: Introduce a callback to flush the local context Julien Grall
2019-03-21 16:36 ` [PATCH RFC 11/14] arm64: Move the ASID allocator code in a separate file Julien Grall
2019-06-05 16:56   ` Julien Grall
2019-06-05 20:41     ` Palmer Dabbelt
2019-06-11  1:56       ` Gary Guo
2019-06-19  8:07     ` Guo Ren
2019-06-19  8:54       ` Julien Grall
2019-06-19  9:12         ` Will Deacon
2019-06-19 12:18           ` Guo Ren
2019-06-19 12:39             ` Will Deacon
2019-06-20  9:33               ` Guo Ren
2019-06-24 10:40                 ` Will Deacon
2019-06-25  7:25                   ` Palmer Dabbelt
2019-09-07 23:52                   ` Guo Ren
2019-09-12 14:02                     ` Will Deacon
2019-09-12 14:59                       ` Guo Ren
2019-09-13  7:13                         ` Guo Ren
2019-09-14  8:49                           ` Guo Ren
2019-09-16 12:57                           ` Jean-Philippe Brucker
2019-09-19 13:07                             ` Guo Ren
2019-09-19 15:18                               ` Jean-Philippe Brucker
2019-09-20  0:07                                 ` Guo Ren
2019-09-20  7:18                                   ` Jean-Philippe Brucker
2019-09-14 14:01                       ` Palmer Dabbelt
2019-09-15  5:03                         ` Anup Patel
2019-09-16 18:18                           ` Will Deacon
2019-09-16 18:28                             ` Palmer Dabbelt
2019-09-17  3:42                             ` Anup Patel
2019-09-19 13:36                               ` Guo Ren
2019-06-19 11:51         ` Guo Ren
2019-06-19 12:52           ` Julien Grall
2019-06-21 14:16           ` Catalin Marinas
2019-06-23 16:35             ` Guo Ren
2019-06-24 10:22               ` Will Deacon [this message]
2019-06-27  9:41                 ` qi.fuli
2019-06-27 10:26                   ` Will Deacon
2019-06-24 15:38               ` Catalin Marinas
2019-06-30  4:29                 ` Guo Ren
2019-07-01  9:17                   ` Catalin Marinas
2019-07-16  3:31                     ` Guo Ren
2019-07-22 16:38                       ` Catalin Marinas
2019-03-21 16:36 ` [PATCH RFC 12/14] arm64/lib: asid: Allow user to update the context under the lock Julien Grall
2019-03-21 16:36 ` [PATCH RFC 13/14] arm/kvm: Introduce a new VMID allocator Julien Grall
2019-03-21 16:36 ` [PATCH RFC 14/14] kvm/arm: Align the VMID allocation with the arm64 ASID one Julien Grall

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