From: Juergen Gross <jgross@suse.com>
To: SF Markus Elfring <elfring@users.sourceforge.net>
Cc: linux-scsi@vger.kernel.org, kernel-janitors@vger.kernel.org,
LKML <linux-kernel@vger.kernel.org>,
Julia Lawall <julia.lawall@lip6.fr>,
David Vrabel <david.vrabel@citrix.com>,
xen-devel@lists.xenproject.org,
Boris Ostrovsky <boris.ostrovsky@oracle.com>
Subject: Re: [PATCH 2/3] xen-scsiback: One function call less in scsiback_device_action() after error detection
Date: Wed, 20 Jul 2016 07:26:31 +0200 [thread overview]
Message-ID: <85b948e0-bf37-dff0-6792-77b5dacef9a0__3248.4526666396$1468992477$gmane$org@suse.com> (raw)
In-Reply-To: <18256bfc-c6f9-8802-8d7d-55766f0b3624@users.sourceforge.net>
On 20/07/16 07:10, SF Markus Elfring wrote:
>>>>> @@ -606,7 +606,7 @@ static void scsiback_device_action(struct vscsibk_pend *pending_req,
>>>>> tmr = kzalloc(sizeof(struct scsiback_tmr), GFP_KERNEL);
>>>>> if (!tmr) {
>>>>> target_put_sess_cmd(se_cmd);
>>>>> - goto err;
>>>>> + goto do_resp;
>>>>> }
>>>>
>>>> Hmm, I'm not convinced this is an improvement.
>>>>
>>>> I'd rather rename the new error label to "put_cmd" and get rid of the
>>>> braces in above if statement:
>>>>
>>>> - if (!tmr) {
>>>> - target_put_sess_cmd(se_cmd);
>>>> - goto err;
>>>> - }
>>>> + if (!tmr)
>>>> + goto put_cmd;
>>>>
>>>> and then in the error path:
>>>>
>>>> -err:
>>>> +put_cmd:
>>>> + target_put_sess_cmd(se_cmd);
>>>
>>> I am unsure on the relevance of this function on such a source position.
>>> Would it make sense to move it further down at the end?
>>
>> You only want to call it in the first error case (allocation failure).
>
> Thanks for your clarification.
>
> I find that my update suggestion (from Saturday) is still appropriate
> in this case.
> https://lkml.org/lkml/2016/7/16/172
And I still think it isn't an improvement: Nack
>>>> +free_tmr:
>>>> kfree(tmr);
>>>
>>> How do you think about to skip this function call after a memory
>>> allocation failure?
>>
>> I think this just doesn't matter. If it were a hot path, yes. But trying
>> to do micro-optimizations in an error path is just not worth the effort.
>
> Would you like to reduce also the amount of function calls in such special
> run-time situations?
I just don't care for the extra 2 or 3 nsecs. Readability is more
important here.
>> I like a linear error path containing all the needed cleanups best.
>
> I would prefer to keep the discussed single function call within
> the basic block of the if statement.
>
> Have we got different opinions about the shown implementation details?
Yes.
Juergen
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next prev parent reply other threads:[~2016-07-20 5:26 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <5307CAA2.8060406@users.sourceforge.net>
[not found] ` <alpine.DEB.2.02.1402212321410.2043@localhost6.localdomain6>
[not found] ` <530A086E.8010901@users.sourceforge.net>
[not found] ` <alpine.DEB.2.02.1402231635510.1985@localhost6.localdomain6>
[not found] ` <530A72AA.3000601@users.sourceforge.net>
[not found] ` <alpine.DEB.2.02.1402240658210.2090@localhost6.localdomain6>
[not found] ` <530B5FB6.6010207@users.sourceforge.net>
[not found] ` <alpine.DEB.2.10.1402241710370.2074@hadrien>
[not found] ` <530C5E18.1020800@users.sourceforge.net>
[not found] ` <alpine.DEB.2.10.1402251014170.2080@hadrien>
[not found] ` <530CD2C4.4050903@users.sourceforge.net>
[not found] ` <alpine.DEB.2.10.1402251840450.7035@hadrien>
[not found] ` <530CF8FF.8080600@users.sourceforge.net>
[not found] ` <alpine.DEB.2.02.1402252117150.2047@localhost6.localdomain6>
[not found] ` <530DD06F.4090703@users.sourceforge.net>
[not found] ` <alpine.DEB.2.02.1402262129250.2221@localhost6.localdomain6>
[not found] ` <5317A59D.4@users.sourceforge.net>
2014-11-02 15:12 ` [PATCH 1/1] PCI: Deletion of unnecessary checks before three function calls SF Markus Elfring
[not found] ` <545649DE.80304@users.sourceforge.net>
2014-11-11 4:07 ` Bjorn Helgaas
2016-07-16 20:20 ` [PATCH 0/3] xen-scsiback: Fine-tuning for scsiback_device_action() SF Markus Elfring
[not found] ` <59e51c7d-f7bb-c55f-d2fe-06dccfef6a99@users.sourceforge.net>
2016-07-16 20:22 ` [PATCH 1/3] xen-scsiback: Delete an unnecessary check before the function call "kfree" SF Markus Elfring
2016-07-16 20:23 ` [PATCH 2/3] xen-scsiback: One function call less in scsiback_device_action() after error detection SF Markus Elfring
2016-07-16 20:24 ` [PATCH 3/3] xen-scsiback: Pass a failure indication as a constant SF Markus Elfring
[not found] ` <fa839c03-b076-0264-c363-5581d0298632@users.sourceforge.net>
2016-07-18 5:01 ` [PATCH 1/3] xen-scsiback: Delete an unnecessary check before the function call "kfree" Juergen Gross
[not found] ` <e447cf62-ffc7-4b82-cff2-947c8874756a@users.sourceforge.net>
2016-07-18 5:05 ` [PATCH 3/3] xen-scsiback: Pass a failure indication as a constant Juergen Gross
[not found] ` <87e55a72-71ad-d0a1-b936-12565bbc6508@users.sourceforge.net>
2016-07-18 5:11 ` [PATCH 2/3] xen-scsiback: One function call less in scsiback_device_action() after error detection Juergen Gross
[not found] ` <fb5824ad-fb09-e471-7dc4-3e32564cc334@suse.com>
2016-07-19 14:56 ` SF Markus Elfring
2016-07-20 4:35 ` Juergen Gross
[not found] ` <83b0b1e2-900b-eefc-160b-7d837730571c@suse.com>
2016-07-20 5:10 ` SF Markus Elfring
2016-07-20 5:26 ` Juergen Gross [this message]
[not found] ` <85b948e0-bf37-dff0-6792-77b5dacef9a0@suse.com>
2016-07-20 11:27 ` [PATCH v2 0/3] xen-scsiback: Fine-tuning for scsiback_device_action() SF Markus Elfring
2016-07-20 11:30 ` [PATCH v2 1/3] xen-scsiback: Delete an unnecessary check before the function call "kfree" SF Markus Elfring
2016-07-20 11:44 ` Juergen Gross
2016-07-20 11:34 ` [PATCH v2 2/3] xen-scsiback: Rename jump labels in scsiback_device_action() SF Markus Elfring
2016-07-20 11:45 ` Juergen Gross
2016-07-20 11:36 ` [PATCH v2 3/3] xen-scsiback: Pass a failure indication as a constant SF Markus Elfring
2016-07-20 11:44 ` Juergen Gross
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