netdev - Re: [PATCH 2/2] iw_cxgb4: add fast-path for small REG

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Date:   Sun, 18 Sep 2016 17:22:42 +0300
From:   Leon Romanovsky <leonro@...n.nu>
To:     Steve Wise <swise@...ngridcomputing.com>
Cc:     dledford@...hat.com, davem@...emloft.net, netdev@...r.kernel.org,
        linux-rdma@...r.kernel.org
Subject: Re: [PATCH 2/2] iw_cxgb4: add fast-path for small REG_MR operations

On Fri, Sep 16, 2016 at 07:54:52AM -0700, Steve Wise wrote:
> When processing a REG_MR work request, if fw supports the
> FW_RI_NSMR_TPTE_WR work request, and if the page list for this
> registration is <= 2 pages, and the current state of the mr is INVALID,
> then use FW_RI_NSMR_TPTE_WR to pass down a fully populated TPTE for FW
> to write.  This avoids FW having to do an async read of the TPTE blocking
> the SQ until the read completes.
>
> To know if the current MR state is INVALID or not, iw_cxgb4 must track the
> state of each fastreg MR.  The c4iw_mr struct state is updated as REG_MR
> and LOCAL_INV WRs are posted and completed, when a reg_mr is destroyed,
> and when RECV completions are processed that include a local invalidation.
>
> This optimization increases small IO IOPS for both iSER and NVMF.
>
> Signed-off-by: Steve Wise <swise@...ngridcomputing.com>
> ---

<...>

> +			      struct ib_reg_wr *wr, struct c4iw_mr *mhp,
> +			      u8 *len16)
> +{
> +	__be64 *p = (__be64 *)fr->pbl;
> +
> +	fr->r2 = cpu_to_be32(0);

Is there any difference between the line above and "fr->r2 = 0"?

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