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[46.135.3.109]) by smtp.gmail.com with ESMTPSA id i13-20020a5d55cd000000b003313426f136sm10142299wrw.39.2023.11.19.23.41.43 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 19 Nov 2023 23:41:45 -0800 (PST) Date: Mon, 20 Nov 2023 08:41:06 +0100 From: Mateusz Guzik To: kernel test robot Cc: Christian Brauner , oe-lkp@lists.linux.dev, lkp@intel.com, linux-kernel@vger.kernel.org, Jann Horn , Linus Torvalds , linux-doc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, intel-gfx@lists.freedesktop.org, linux-fsdevel@vger.kernel.org, gfs2@lists.linux.dev, bpf@vger.kernel.org, ying.huang@intel.com, feng.tang@intel.com, fengwei.yin@intel.com Subject: Re: [linus:master] [file] 0ede61d858: will-it-scale.per_thread_ops -2.9% regression Message-ID: References: <202311201406.2022ca3f-oliver.sang@intel.com> Precedence: bulk X-Mailing-List: gfs2@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <202311201406.2022ca3f-oliver.sang@intel.com> On Mon, Nov 20, 2023 at 03:11:31PM +0800, kernel test robot wrote: > > > Hello, > > kernel test robot noticed a -2.9% regression of will-it-scale.per_thread_ops on: > > > commit: 0ede61d8589cc2d93aa78230d74ac58b5b8d0244 ("file: convert to SLAB_TYPESAFE_BY_RCU") > https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git master > > 93faf426e3cc000c 0ede61d8589cc2d93aa78230d74 > ---------------- --------------------------- > %stddev %change %stddev > \ | \ [snip] > 30.90 ± 4% -20.6 10.35 ± 2% perf-profile.self.cycles-pp.__fget_light > 0.00 +26.5 26.48 perf-profile.self.cycles-pp.__get_file_rcu [snip] So __fget_light now got a func call. I don't know if this is worth patching (and benchmarking after), but I if sorting this out is of interest, triviality below is probably the easiest way out: diff --git a/fs/file.c b/fs/file.c index 5fb0b146e79e..d8d3e18800c4 100644 --- a/fs/file.c +++ b/fs/file.c @@ -856,14 +856,14 @@ void do_close_on_exec(struct files_struct *files) spin_unlock(&files->file_lock); } -static struct file *__get_file_rcu(struct file __rcu **f) +static __always_inline struct file *__get_file_rcu(struct file __rcu **f) { struct file __rcu *file; struct file __rcu *file_reloaded; struct file __rcu *file_reloaded_cmp; file = rcu_dereference_raw(*f); - if (!file) + if (unlikely(!file)) return NULL; if (unlikely(!atomic_long_inc_not_zero(&file->f_count))) @@ -891,7 +891,7 @@ static struct file *__get_file_rcu(struct file __rcu **f) * If the pointers don't match the file has been reallocated by * SLAB_TYPESAFE_BY_RCU. */ - if (file == file_reloaded_cmp) + if (likely(file == file_reloaded_cmp)) return file_reloaded; fput(file);