linux-kernel - Re: [PATCH] RDMA/core: reduce IB_POLL

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Date:   Tue, 20 Feb 2018 21:14:29 +0000
From:   Bart Van Assche <Bart.VanAssche@....com>
To:     "jgg@...pe.ca" <jgg@...pe.ca>, "arnd@...db.de" <arnd@...db.de>,
        "dledford@...hat.com" <dledford@...hat.com>
CC:     Bart Van Assche <Bart.VanAssche@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "leonro@...lanox.com" <leonro@...lanox.com>,
        "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
        "sagi@...mberg.me" <sagi@...mberg.me>
Subject: Re: [PATCH] RDMA/core: reduce IB_POLL_BATCH constant

On Tue, 2018-02-20 at 21:59 +0100, Arnd Bergmann wrote:
>  /* # of WCs to poll for with a single call to ib_poll_cq */
> -#define IB_POLL_BATCH			16
> +#define IB_POLL_BATCH			8

The purpose of batch polling is to minimize contention on the cq spinlock.
Reducing the IB_POLL_BATCH constant may affect performance negatively. Has
the performance impact of this change been verified for all affected drivers
(ib_srp, ib_srpt, ib_iser, ib_isert, NVMeOF, NVMeOF target, SMB Direct, NFS
over RDMA, ...)?

Bart.