linux-kernel - Re: [PATCH 2/6] dma: bcm-sba-raid: Peek mbox when we are left with no free requests

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Date:   Fri, 28 Jul 2017 09:09:45 +0530
From:   Anup Patel <anup.patel@...adcom.com>
To:     Vinod Koul <vinod.koul@...el.com>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Dan Williams <dan.j.williams@...el.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Scott Branden <sbranden@...adcom.com>,
        Ray Jui <rjui@...adcom.com>,
        Linux Kernel <linux-kernel@...r.kernel.org>,
        Linux ARM Kernel <linux-arm-kernel@...ts.infradead.org>,
        Device Tree <devicetree@...r.kernel.org>,
        dmaengine@...r.kernel.org,
        BCM Kernel Feedback <bcm-kernel-feedback-list@...adcom.com>
Subject: Re: [PATCH 2/6] dma: bcm-sba-raid: Peek mbox when we are left with no
 free requests

On Fri, Jul 28, 2017 at 8:45 AM, Vinod Koul <vinod.koul@...el.com> wrote:
> On Thu, Jul 27, 2017 at 10:25:25AM +0530, Anup Patel wrote:
>> On Wed, Jul 26, 2017 at 10:40 PM, Vinod Koul <vinod.koul@...el.com> wrote:
>> > On Wed, Jul 26, 2017 at 11:06:40AM +0530, Anup Patel wrote:
>> >> We should peek mbox channels when we are left with no free
>> >> sba_requests in sba_alloc_request()
>> >
>> > and why is the world should we do that, how does that help??
>>
>> When setting up RAID array on several NVMe disk we observed
>> that sba_alloc_request() start failing (due to no free requests left)
>> and RAID array setup becomes very slow.
>>
>> Doing mbox channel peek when we have no free requests left,
>> improves performance of RAID array setup.
>
> How about documenting this tribal knowledge in the changelog. Changelogs are
> very useful, 6 months down the line, you will struggle to remember why this
> was changed..

Sure, I will have detailed commit description for this.

Regards,
Anup