From: Nadav Amit <namit@vmware.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Andy Lutomirski <luto@kernel.org>,
Dave Hansen <dave.hansen@linux.intel.com>,
Rik van Riel <riel@surriel.com>,
Josh Poimboeuf <jpoimboe@redhat.com>
Subject: Re: [PATCH v5 1/8] smp: Run functions concurrently in smp_call_function_many_cond()
Date: Tue, 16 Feb 2021 18:53:09 +0000 [thread overview]
Message-ID: <457D8FBC-8F64-48E9-B9E2-1A316DB0C2B6@vmware.com> (raw)
In-Reply-To: <YCvztEk6sqiCxXZV@hirez.programming.kicks-ass.net>
> On Feb 16, 2021, at 8:32 AM, Peter Zijlstra <peterz@infradead.org> wrote:
>
> On Tue, Feb 09, 2021 at 02:16:46PM -0800, Nadav Amit wrote:
>> From: Nadav Amit <namit@vmware.com>
>>
>> Currently, on_each_cpu() and similar functions do not exploit the
>> potential of concurrency: the function is first executed remotely and
>> only then it is executed locally. Functions such as TLB flush can take
>> considerable time, so this provides an opportunity for performance
>> optimization.
>>
>> To do so, modify smp_call_function_many_cond(), to allows the callers to
>> provide a function that should be executed (remotely/locally), and run
>> them concurrently. Keep other smp_call_function_many() semantic as it is
>> today for backward compatibility: the called function is not executed in
>> this case locally.
>>
>> smp_call_function_many_cond() does not use the optimized version for a
>> single remote target that smp_call_function_single() implements. For
>> synchronous function call, smp_call_function_single() keeps a
>> call_single_data (which is used for synchronization) on the stack.
>> Interestingly, it seems that not using this optimization provides
>> greater performance improvements (greater speedup with a single remote
>> target than with multiple ones). Presumably, holding data structures
>> that are intended for synchronization on the stack can introduce
>> overheads due to TLB misses and false-sharing when the stack is used for
>> other purposes.
>>
>> Reviewed-by: Dave Hansen <dave.hansen@linux.intel.com>
>> Cc: Peter Zijlstra <peterz@infradead.org>
>> Cc: Rik van Riel <riel@surriel.com>
>> Cc: Thomas Gleixner <tglx@linutronix.de>
>> Cc: Andy Lutomirski <luto@kernel.org>
>> Cc: Josh Poimboeuf <jpoimboe@redhat.com>
>> Signed-off-by: Nadav Amit <namit@vmware.com>
>
> Kernel-CI is giving me a regression that's most likely this patch:
>
> https://nam04.safelinks.protection.outlook.com/?url=https%3A%2F%2Fkernelci.org%2Ftest%2Fcase%2Fid%2F602bdd621c979f83faaddcc6%2F&data=04%7C01%7Cnamit%40vmware.com%7C7dc93f3b74d8488de06f08d8d2988b0a%7Cb39138ca3cee4b4aa4d6cd83d9dd62f0%7C0%7C0%7C637490899907612612%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=PFs0ydMLh6xVfAQzAxSNd108YjxKMopNwxqsm82lEog%3D&reserved=0
>
> I'm not sure I can explain it yet. It did get me looking at
> on_each_cpu() and it appears that wants to be converted too, something
> like the below perhaps.
Looks like a good cleanup, but I cannot say I understand the problem and how
it would solve it. Err...
next prev parent reply other threads:[~2021-02-16 18:54 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-09 22:16 [PATCH v5 0/8] x86/tlb: Concurrent TLB flushes Nadav Amit
2021-02-09 22:16 ` [PATCH v5 1/8] smp: Run functions concurrently in smp_call_function_many_cond() Nadav Amit
2021-02-16 12:04 ` Peter Zijlstra
2021-02-16 18:49 ` Nadav Amit
2021-02-16 12:06 ` Peter Zijlstra
2021-02-16 16:32 ` Peter Zijlstra
2021-02-16 18:53 ` Nadav Amit [this message]
2021-02-16 18:59 ` Peter Zijlstra
2021-02-16 19:04 ` Nadav Amit
2021-02-17 1:02 ` Nadav Amit
2021-02-18 12:55 ` Peter Zijlstra
2021-02-18 8:09 ` Christoph Hellwig
2021-02-18 9:36 ` Nadav Amit
2021-02-18 11:12 ` Peter Zijlstra
2021-02-09 22:16 ` [PATCH v5 2/8] x86/mm/tlb: Unify flush_tlb_func_local() and flush_tlb_func_remote() Nadav Amit
2021-02-09 22:16 ` [PATCH v5 3/8] x86/mm/tlb: Open-code on_each_cpu_cond_mask() for tlb_is_not_lazy() Nadav Amit
2021-02-18 8:16 ` Christoph Hellwig
2021-02-18 8:24 ` Nadav Amit
2021-02-18 8:28 ` Christoph Hellwig
2021-02-09 22:16 ` [PATCH v5 4/8] x86/mm/tlb: Flush remote and local TLBs concurrently Nadav Amit
2021-02-16 12:10 ` Peter Zijlstra
2021-02-16 19:17 ` Nadav Amit
2021-02-18 8:14 ` Christoph Hellwig
2021-02-09 22:16 ` [PATCH v5 5/8] x86/mm/tlb: Privatize cpu_tlbstate Nadav Amit
2021-02-09 22:16 ` [PATCH v5 6/8] x86/mm/tlb: Do not make is_lazy dirty for no reason Nadav Amit
2021-02-09 22:16 ` [PATCH v5 7/8] cpumask: Mark functions as pure Nadav Amit
2021-02-16 12:14 ` Peter Zijlstra
2021-02-09 22:16 ` [PATCH v5 8/8] x86/mm/tlb: Remove unnecessary uses of the inline keyword Nadav Amit
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