> -----Original Message----- > From: Anshuman Khandual [mailto:anshuman.khandual@xxxxxxx] > Sent: Tuesday, February 23, 2021 7:10 PM > To: Song Bao Hua (Barry Song) <song.bao.hua@xxxxxxxxxxxxx>; corbet@xxxxxxx; > linux-doc@xxxxxxxxxxxxxxx; akpm@xxxxxxxxxxxxxxxxxxxx; linux-mm@xxxxxxxxx > Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; > linuxarm@xxxxxxxxxxxxx; Mel Gorman <mgorman@xxxxxxx>; Andy Lutomirski > <luto@xxxxxxxxxx>; Catalin Marinas <catalin.marinas@xxxxxxx>; Will Deacon > <will@xxxxxxxxxx> > Subject: [Linuxarm] Re: [PATCH] Documentation/features: mark > BATCHED_UNMAP_TLB_FLUSH doesn't apply to ARM64 > > > > On 2/23/21 6:02 AM, Barry Song wrote: > > BATCHED_UNMAP_TLB_FLUSH is used on x86 to do batched tlb shootdown by > > sending one IPI to TLB flush all entries after unmapping pages rather > > than sending an IPI to flush each individual entry. > > On arm64, tlb shootdown is done by hardware. Flush instructions are > > innershareable. The local flushes are limited to the boot (1 per CPU) > > and when a task is getting a new ASID. > > Is there any previous discussion around this ? I copied the declaration of local flushes from: "ARM64 Linux kernel is SMP-aware (no possibility to build only for UP). Most of the flush instructions are innershareable. The local flushes are limited to the boot (1 per CPU) and when a task is getting a new ASIC." https://patchwork.kernel.org/project/xen-devel/patch/1461756173-10300-1-git-send-email-julien.grall@xxxxxxx/ I am not sure if getting a new asid and the boot are the only two cases of local flushes while I think this is probably true. But even we find more corner cases, hardly the trend arm64 doesn't need BATCHED_UNMAP_TLB_FLUSH will be changed. > > > So marking this feature as "TODO" is not proper. ".." isn't good as > > well. So this patch adds a "N/A" for this kind of features which are > > not needed on some architectures. > > > > Cc: Mel Gorman <mgorman@xxxxxxx> > > Cc: Andy Lutomirski <luto@xxxxxxxxxx> > > Cc: Catalin Marinas <catalin.marinas@xxxxxxx> > > Cc: Will Deacon <will@xxxxxxxxxx> > > Signed-off-by: Barry Song <song.bao.hua@xxxxxxxxxxxxx> > > --- > > Documentation/features/arch-support.txt | 1 + > > Documentation/features/vm/TLB/arch-support.txt | 2 +- > > 2 files changed, 2 insertions(+), 1 deletion(-) > > > > diff --git a/Documentation/features/arch-support.txt > b/Documentation/features/arch-support.txt > > index d22a1095e661..118ae031840b 100644 > > --- a/Documentation/features/arch-support.txt > > +++ b/Documentation/features/arch-support.txt > > @@ -8,4 +8,5 @@ The meaning of entries in the tables is: > > | ok | # feature supported by the architecture > > |TODO| # feature not yet supported by the architecture > > | .. | # feature cannot be supported by the hardware > > + | N/A| # feature doesn't apply to the architecture > > NA might be better here. s/doesn't apply/not applicable/ in order to match NA. > Still wondering if NA is really needed when there is already ".." ? Regardless > either way should be fine. I don't think ".." is proper here. ".." means hardware doesn't support the feature. But here it is just opposite, arm64 has the hardware support of tlb shootdown rather than depending on a software IPI. > > > > > diff --git a/Documentation/features/vm/TLB/arch-support.txt > b/Documentation/features/vm/TLB/arch-support.txt > > index 30f75a79ce01..0d070f9f98d8 100644 > > --- a/Documentation/features/vm/TLB/arch-support.txt > > +++ b/Documentation/features/vm/TLB/arch-support.txt > > @@ -9,7 +9,7 @@ > > | alpha: | TODO | > > | arc: | TODO | > > | arm: | TODO | > > - | arm64: | TODO | > > + | arm64: | N/A | > > | c6x: | .. | > > | csky: | TODO | > > | h8300: | .. | > > Thanks Barry
