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Sender: Guenter Roeck <groeck7@gmail.com>
Date:   Sun, 29 Oct 2023 10:05:39 -0700
From:   Guenter Roeck <linux@roeck-us.net>
To:     "wuqiang.matt" <wuqiang.matt@bytedance.com>
Cc:     linux-trace-kernel@vger.kernel.org, mhiramat@kernel.org,
        davem@davemloft.net, anil.s.keshavamurthy@intel.com,
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        dan.j.williams@intel.com, jpoimboe@kernel.org,
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Subject: Re: [PATCH v1] lib,kprobes: using try_cmpxchg_local in objpool_push
Message-ID: <b579d68f-f2ec-42ef-8366-6878c9930e0c@roeck-us.net>
References: <20231023112452.6290-1-wuqiang.matt@bytedance.com>
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On Mon, Oct 23, 2023 at 07:24:52PM +0800, wuqiang.matt wrote:
> The objpool_push can only happen on local cpu node, so only the local
> cpu can touch slot->tail and slot->last, which ensures the correctness
> of using cmpxchg without lock prefix (using try_cmpxchg_local instead
> of try_cmpxchg_acquire).
> 
> Testing with IACA found the lock version of pop/push pair costs 16.46
> cycles and local-push version costs 15.63 cycles. Kretprobe throughput
> is improved to 1.019 times of the lock version for x86_64 systems.
> 
> OS: Debian 10 X86_64, Linux 6.6rc6 with freelist
> HW: XEON 8336C x 2, 64 cores/128 threads, DDR4 3200MT/s
> 
>                  1T         2T         4T         8T        16T
>   lock:    29909085   59865637  119692073  239750369  478005250
>   local:   30297523   60532376  121147338  242598499  484620355
>                 32T        48T        64T        96T       128T
>   lock:   957553042 1435814086 1680872925 2043126796 2165424198
>   local:  968526317 1454991286 1861053557 2059530343 2171732306
> 
> Signed-off-by: wuqiang.matt <wuqiang.matt@bytedance.com>

This patch results in

lib/objpool.c:169:12: error: implicit declaration of function 'arch_cmpxchg_local' is invalid in C99

or

lib/objpool.c: In function 'objpool_try_add_slot':
include/linux/atomic/atomic-arch-fallback.h:384:27: error: implicit declaration of function 'arch_cmpxchg_local'

for various architectures (I have seen it with arc, hexagon, and openrisc
so far).

As usual, my apologies for the noise if this has already been reported
and/or fixed.

Guenter