From: "Huang\, Ying" <ying.huang@intel.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: "Huang\, Ying" <ying.huang@intel.com>,
Eric Dumazet <eric.dumazet@gmail.com>,
<linux-kernel@vger.kernel.org>, Ingo Molnar <mingo@kernel.org>,
Michael Ellerman <mpe@ellerman.id.au>,
Borislav Petkov <bp@suse.de>,
Thomas Gleixner <tglx@linutronix.de>,
"Juergen Gross" <jgross@suse.com>, Aaron Lu <aaron.lu@intel.com>
Subject: Re: [PATCH 3/3] IPI: Avoid to use 2 cache lines for one call_single_data
Date: Sat, 05 Aug 2017 08:47:02 +0800 [thread overview]
Message-ID: <87d18alu2h.fsf@yhuang-mobile.sh.intel.com> (raw)
In-Reply-To: <20170804092754.hyhbhyr2r4gonpu4@hirez.programming.kicks-ass.net> (Peter Zijlstra's message of "Fri, 4 Aug 2017 11:27:54 +0200")
Peter Zijlstra <peterz@infradead.org> writes:
> On Fri, Aug 04, 2017 at 10:05:55AM +0800, Huang, Ying wrote:
>> "Huang, Ying" <ying.huang@intel.com> writes:
>> > Peter Zijlstra <peterz@infradead.org> writes:
>
>> >> +struct __call_single_data {
>> >> struct llist_node llist;
>> >> smp_call_func_t func;
>> >> void *info;
>> >> unsigned int flags;
>> >> };
>> >>
>> >> +typedef struct __call_single_data call_single_data_t
>> >> + __aligned(sizeof(struct __call_single_data));
>> >> +
>> >
>> > Another requirement of the alignment is that it should be the power of
>> > 2. Otherwise, for example, if someone adds a field to struct, so that
>> > the size becomes 40 on x86_64. The alignment should be 64 instead of
>> > 40.
>>
>> Thanks Aaron, he reminded me that there is a roundup_pow_of_two(). So
>> the typedef could be,
>>
>> typedef struct __call_single_data call_single_data_t
>> __aligned(roundup_pow_of_two(sizeof(struct __call_single_data));
>>
>
> Yes, that would take away the requirement to play padding games with the
> struct. Then again, maybe its a good thing to have to be explicit about
> it.
>
> If you see:
>
> struct __call_single_data {
> struct llist_node llist;
> smp_call_func_t func;
> void *info
> int flags;
> void *extra_field;
>
> unsigned long __padding[3]; /* make align work */
> };
>
> that makes it very clear what is going on. In any case, we can delay
> this part because the current structure is a power-of-2 for both ILP32
> and LP64. So only the person growing this will have to deal with it ;-)
Yes. That looks good. So you will prepare the final patch? Or you
hope me to do that?
Best Regards,
Huang, Ying
next prev parent reply other threads:[~2017-08-05 0:47 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-08-02 8:52 [PATCH 0/3] IPI: Avoid to use 2 cache lines for one call_single_data Huang, Ying
2017-08-02 8:52 ` [PATCH 1/3] percpu: Add alloc_percpu_aligned() Huang, Ying
2017-08-02 13:50 ` Christopher Lameter
2017-08-03 0:33 ` Huang, Ying
2017-08-02 8:52 ` [PATCH 2/3] iova: Use alloc_percpu_aligned() Huang, Ying
2017-08-02 8:52 ` [PATCH 3/3] IPI: Avoid to use 2 cache lines for one call_single_data Huang, Ying
2017-08-02 10:18 ` Eric Dumazet
2017-08-02 10:53 ` Peter Zijlstra
2017-08-03 8:35 ` Huang, Ying
2017-08-03 8:57 ` Peter Zijlstra
2017-08-04 1:28 ` Huang, Ying
2017-08-04 2:05 ` Huang, Ying
2017-08-04 9:27 ` Peter Zijlstra
2017-08-05 0:47 ` Huang, Ying [this message]
2017-08-07 8:28 ` Peter Zijlstra
2017-08-08 4:30 ` Huang, Ying
2017-08-14 5:44 ` Huang, Ying
2017-08-28 5:19 ` Huang, Ying
2017-08-28 8:49 ` Peter Zijlstra
2017-08-29 14:23 ` [tip:locking/core] smp: Avoid using two cache lines for struct call_single_data tip-bot for Ying Huang
2017-08-04 9:20 ` [PATCH 3/3] IPI: Avoid to use 2 cache lines for one call_single_data Peter Zijlstra
2017-08-02 13:54 ` [PATCH 0/3] " Christopher Lameter
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