linux-kernel - Re: [RFC] Is lib/irq_poll still considered useful?

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Message-ID: <20211001064110.anckzkd5ymnxvczc@linutronix.de>
Date:   Fri, 1 Oct 2021 08:41:10 +0200
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     linux-kernel@...r.kernel.org, linux-scsi@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Doug Ledford <dledford@...hat.com>,
        Jason Gunthorpe <jgg@...pe.ca>, linux-rdma@...r.kernel.org,
        Subbu Seetharaman <subbu.seetharaman@...adcom.com>,
        Ketan Mukadam <ketan.mukadam@...adcom.com>,
        Jitendra Bhivare <jitendra.bhivare@...adcom.com>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        "Manoj N. Kumar" <manoj@...ux.ibm.com>,
        "Matthew R. Ochs" <mrochs@...ux.ibm.com>,
        Uma Krishnan <ukrishn@...ux.ibm.com>,
        Brian King <brking@...ibm.com>,
        James Smart <james.smart@...adcom.com>,
        Dick Kennedy <dick.kennedy@...adcom.com>,
        Kashyap Desai <kashyap.desai@...adcom.com>,
        Sumit Saxena <sumit.saxena@...adcom.com>,
        Shivasharan S <shivasharan.srikanteshwara@...adcom.com>,
        megaraidlinux.pdl@...adcom.com,
        Sathya Prakash <sathya.prakash@...adcom.com>,
        Sreekanth Reddy <sreekanth.reddy@...adcom.com>,
        Suganath Prabu Subramani 
        <suganath-prabu.subramani@...adcom.com>,
        MPT-FusionLinux.pdl@...adcom.com
Subject: Re: [RFC] Is lib/irq_poll still considered useful?

On 2021-10-01 05:24:49 [+0100], Christoph Hellwig wrote:
> On Thu, Sep 30, 2021 at 12:56:05PM +0200, Sebastian Andrzej Siewior wrote:
> > Is there a reason for the remaining user of irq_poll to keep using it?
> 
> At least for RDMA there are workloads where the latency difference
> matters.  That's why we added both the irq_poll and workqueue mode
> to thew new CQ API a few years ago.

Would it work for them to move to threaded interrupts or is the NAPI
like behaviour (delay after a while to the next jiffy) the killer
feature?

Sebastian