linux-kernel - Re: [PATCH V2] nvme-pci: assign separate irq vectors for adminq and ioq0

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <66e4ad3e-4019-13ec-94c0-e168cc1d95b4@oracle.com>
Date:   Thu, 1 Mar 2018 18:05:53 +0800
From:   "jianchao.wang" <jianchao.w.wang@...cle.com>
To:     Sagi Grimberg <sagi@...mberg.me>, Christoph Hellwig <hch@....de>
Cc:     keith.busch@...el.com, axboe@...com, linux-kernel@...r.kernel.org,
        linux-nvme@...ts.infradead.org
Subject: Re: [PATCH V2] nvme-pci: assign separate irq vectors for adminq and
 ioq0

Hi sagi

Thanks for your kindly response.

On 03/01/2018 05:28 PM, Sagi Grimberg wrote:
> 
>> Note that we originally allocates irqs this way, and Keith changed
>> it a while ago for good reasons.  So I'd really like to see good
>> reasons for moving away from this, and some heuristics to figure
>> out which way to use.  E.g. if the device supports more irqs than
>> I/O queues your scheme might always be fine.
> 
> I still don't understand what this buys us in practice. Seems redundant
> to allocate another vector without any (even marginal) difference.
> 

When the adminq is free, ioq0 irq completion path has to invoke nvme_irq twice, one for itself,
one for adminq completion irq action.
We are trying to save every cpu cycle across the nvme host path, why we waste nvme_irq cycles here.
If we have enough vectors, we could allocate another irq vector for adminq to avoid this.

Sincerely
Jianchao