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From: Dan Williams <dan.j.williams@intel.com>
To: Boaz Harrosh <boaz@plexistor.com>
Cc: Christoph Hellwig <hch@lst.de>, Jens Axboe <axboe@kernel.dk>,
	linux-nvdimm <linux-nvdimm@ml01.01.org>, X86 ML <x86@kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>
Subject: Re: [Linux-nvdimm] [PATCH 4/6] SQUSHME: pmem: Micro cleaning
Date: Tue, 31 Mar 2015 08:30:57 -0700	[thread overview]
Message-ID: <CAPcyv4iBjN6h_o+---mt9b5nXr-mC_famL_Od9PCDZByz959MQ@mail.gmail.com> (raw)
In-Reply-To: <551ABC26.3000008@plexistor.com>

On Tue, Mar 31, 2015 at 8:24 AM, Boaz Harrosh <boaz@plexistor.com> wrote:
> On 03/31/2015 06:17 PM, Dan Williams wrote:
>> On Tue, Mar 31, 2015 at 6:27 AM, Boaz Harrosh <boaz@plexistor.com> wrote:
>>>
>>> Some error checks had unlikely some did not. Put unlikely
>>> on all error handling paths.
>>> (I like unlikely for error paths specially for readability)
>>
>> "unlikely()" is not a readability hint, it's specifically for branches
>> that profiling shows adding it makes a difference.  Just delete them
>> all until profiling show they make a difference.  They certainly don't
>> make a difference in the slow paths.
>>
>
> Why?

Because the compiler and cpu already does a decent job, and if you get
the frequency wrong it can hurt performance [1].

It's pre-mature optimization to sprinkle them around, especially in slow paths.

[1]: https://lwn.net/Articles/420019/

  reply	other threads:[~2015-03-31 15:31 UTC|newest]

Thread overview: 69+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-03-26  8:32 another pmem variant V2 Christoph Hellwig
2015-03-26  8:32 ` [PATCH 1/3] pmem: Initial version of persistent memory driver Christoph Hellwig
2015-03-26 14:12   ` [Linux-nvdimm] " Dan Williams
2015-03-26 14:35     ` Christoph Hellwig
2015-03-26 21:37       ` Ross Zwisler
2015-03-26 14:52     ` Boaz Harrosh
2015-03-26 15:59       ` Dan Williams
2015-03-26  8:32 ` [PATCH 2/3] x86: add a is_e820_ram() helper Christoph Hellwig
2015-03-26  9:02   ` Ingo Molnar
2015-03-26  9:34     ` Christoph Hellwig
2015-03-26 10:04       ` Ingo Molnar
2015-03-26 10:19         ` Christoph Hellwig
2015-03-26 10:28           ` Ingo Molnar
2015-03-26 10:29             ` Christoph Hellwig
2015-03-26 15:49       ` Boaz Harrosh
2015-03-26 16:02         ` [Linux-nvdimm] " Dan Williams
2015-03-26 16:07           ` Boaz Harrosh
2015-03-26 16:43         ` Christoph Hellwig
2015-03-26 18:46           ` Elliott, Robert (Server Storage)
2015-03-26 19:25             ` [Linux-nvdimm] " Dan Williams
2015-03-26 20:53           ` Ross Zwisler
2015-03-26 22:59       ` Yinghai Lu
2015-03-27  8:10         ` Christoph Hellwig
2015-03-26  8:32 ` [PATCH 3/3] x86: add support for the non-standard protected e820 type Christoph Hellwig
2015-03-26 16:57 ` another pmem variant V2 Boaz Harrosh
2015-03-26 17:02   ` [PATCH] SQUASHME: Streamline pmem.c Boaz Harrosh
2015-03-26 17:23     ` Christoph Hellwig
2015-03-26 22:17     ` Ross Zwisler
2015-03-26 22:22     ` Ross Zwisler
2015-03-26 23:31     ` [Linux-nvdimm] " Dan Williams
2015-03-31 13:44       ` Boaz Harrosh
2015-03-26 17:18   ` another pmem variant V2 Christoph Hellwig
2015-03-26 17:31     ` Boaz Harrosh
2015-03-26 18:38       ` Christoph Hellwig
2015-03-31  9:25   ` Christoph Hellwig
2015-03-31 10:25     ` Boaz Harrosh
2015-03-31 10:31       ` Boaz Harrosh
2015-03-31 14:21       ` [RFC] SQUASHME: pmem: Split up pmem_probe from pmem_alloc Boaz Harrosh
2015-03-31 16:10         ` Christoph Hellwig
2015-03-31 16:08       ` another pmem variant V2 Christoph Hellwig
2015-03-31 13:18     ` [SQUASHME 0/6] Streamline of Initial pmem submission Boaz Harrosh
2015-03-31 13:23       ` [PATCH 1/6] SQUASHME: Don't let e820_PMEM sections Boaz Harrosh
2015-03-31 17:16         ` [Linux-nvdimm] " Brooks, Adam J
2015-03-31 13:24       ` [PATCH 2/6] SQUASHME: pmem: Remove getgeo Boaz Harrosh
2015-03-31 13:25       ` [PATCH 3/6] SQUASHME: pmem: Streamline pmem driver Boaz Harrosh
2015-03-31 13:27       ` [PATCH 4/6] SQUSHME: pmem: Micro cleaning Boaz Harrosh
2015-03-31 15:17         ` [Linux-nvdimm] " Dan Williams
2015-03-31 15:24           ` Boaz Harrosh
2015-03-31 15:30             ` Dan Williams [this message]
2015-03-31 15:43               ` Boaz Harrosh
2015-03-31 19:40                 ` Matthew Wilcox
2015-03-31 13:28       ` [PATCH 5/6] SQUASHME: pmem: Remove SECTOR_SHIFT Boaz Harrosh
2015-03-31 13:33       ` [PATCH 6/6] SQUASHME: pmem: Remove "... based on brd.c" + Copyright Boaz Harrosh
2015-03-31 15:14     ` another pmem variant V2 Boaz Harrosh
2015-03-31 16:16       ` Christoph Hellwig
2015-03-31 16:44         ` Ingo Molnar
2015-03-31 17:24           ` Christoph Hellwig
2015-03-31 17:33             ` [Linux-nvdimm] " Dan Williams
2015-04-01  7:50               ` Ingo Molnar
2015-04-01  8:06                 ` Boaz Harrosh
2015-04-01 12:49         ` Boaz Harrosh
2015-03-31 22:11 ` Elliott, Robert (Server Storage)
2015-04-01  7:26   ` Christoph Hellwig
2015-04-02 15:11     ` Elliott, Robert (Server Storage)
2015-04-02 16:41       ` Christoph Hellwig
2015-04-02 18:03         ` Ingo Molnar
2015-04-02 18:03           ` Ingo Molnar
2015-04-01 19:33 ` Elliott, Robert (Server Storage)
2015-04-02  9:37   ` Christoph Hellwig

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