linux-kernel - Re:[PATCH 2/2] powerpc/locking: enable HAVE_CMPXCHG

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Message-ID: <tencent_0161BE863378EC161A2CF685@qq.com>
Date: Thu, 22 Aug 2024 16:31:09 +0800
From: "虞陆铭" <luming.yu@...ngroup.cn>
To: "虞陆铭" <luming.yu@...ngroup.cn>, "linuxppc-dev" <linuxppc-dev@...ts.ozlabs.org>, "linux-kernel" <linux-kernel@...r.kernel.org>, "mpe" <mpe@...erman.id.au>, "npiggin" <npiggin@...il.com>, "christophe.leroy" <christophe.leroy@...roup.eu>
Subject: Re:[PATCH 2/2] powerpc/locking: enable HAVE_CMPXCHG_LOCAL in kconfig

(in text)

Hi,

specific for local cmpxchg enabled on p8 powernv platform on which the patch enabled vm_state update path,
ftrace data below indicates it is  at the level  ofabout 4us or 5us latency,  for such a big cache cold operations.
          <...>-277787  [008] ..... 88366.233643: refresh_cpu_vm_stats <-vmstat_update
          <idle>-0       [008] d.... 88366.233648: tick_nohz_idle_stop_tick <-do_idle

I have no diff data against the latency without the patch. But based on the estimation of the pipeline overhead for
such a big operation incurred by the vm stats update, it looks not bad.
 I will do more testing and collect more histogram for different scenarios to ensure that
the latency level of understanding is something statistically make sense.

Just for the record that the small patch works as expected. :-)

BR
Luming
 
 
------------------ Original ------------------
From:  "虞陆铭"<luming.yu@...ngroup.cn>;
Date:  Mon, Dec 4, 2023 10:23 AM
To:  "linuxppc-dev"<linuxppc-dev@...ts.ozlabs.org>; "linux-kernel"<linux-kernel@...r.kernel.org>; "mpe"<mpe@...erman.id.au>; "npiggin"<npiggin@...il.com>; "christophe.leroy"<christophe.leroy@...roup.eu>; 
Cc:  "luming.yu"<luming.yu@...il.com>; "ke.zhao"<ke.zhao@...ngroup.cn>; "dawei.li"<dawei.li@...ngroup.cn>; "shenghui.qu"<shenghui.qu@...ngroup.cn>; "虞陆铭"<luming.yu@...ngroup.cn>; 
Subject:  [PATCH 2/2] powerpc/locking: enable HAVE_CMPXCHG_LOCAL in kconfig

 

enable arch feature HAVE_CMPXCHG_LOCAL for ppc by default

Signed-off-by: Luming Yu <luming.yu@...ngroup.cn>
---
 arch/powerpc/Kconfig | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 6f105ee4f3cf..c10229c0243c 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -226,6 +226,7 @@ config PPC
 	select HAVE_ARCH_SECCOMP_FILTER
 	select HAVE_ARCH_TRACEHOOK
 	select HAVE_ASM_MODVERSIONS
+	select HAVE_CMPXCHG_LOCAL
 	select HAVE_CONTEXT_TRACKING_USER
 	select HAVE_C_RECORDMCOUNT
 	select HAVE_DEBUG_KMEMLEAK
-- 
2.42.0.windows.2