linux-kernel - Re: [PATCH v2 11/16] dmaengine: bcm-sba-raid: Peek mbox when we have no free requests

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Message-ID: <20170817064008.GB3053@localhost>
Date:   Thu, 17 Aug 2017 12:10:08 +0530
From:   Vinod Koul <vinod.koul@...el.com>
To:     Anup Patel <anup.patel@...adcom.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@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, devicetree@...r.kernel.org,
        dmaengine@...r.kernel.org, bcm-kernel-feedback-list@...adcom.com
Subject: Re: [PATCH v2 11/16] dmaengine: bcm-sba-raid: Peek mbox when we have
 no free requests

On Tue, Aug 01, 2017 at 04:07:55PM +0530, Anup Patel wrote:
> When setting up RAID array on several NVMe disks we observed that
> sba_alloc_request() start failing (due to no free requests left)
> and RAID array setup becomes very slow.
> 
> To improve performance, we do mbox channel peek when we have
> no free requests. This improves performance of RAID array setup
> because mbox requests that were completed but not processed by
> mbox completion worker will be processed immediately by mbox
> channel peek.
> 
> Signed-off-by: Anup Patel <anup.patel@...adcom.com>
> Reviewed-by: Ray Jui <ray.jui@...adcom.com>
> Reviewed-by: Scott Branden <scott.branden@...adcom.com>
> ---
>  drivers/dma/bcm-sba-raid.c | 25 ++++++++++++++++++++-----
>  1 file changed, 20 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/dma/bcm-sba-raid.c b/drivers/dma/bcm-sba-raid.c
> index f14ed0a..399250e 100644
> --- a/drivers/dma/bcm-sba-raid.c
> +++ b/drivers/dma/bcm-sba-raid.c
> @@ -200,6 +200,14 @@ static inline u32 __pure sba_cmd_pq_c_mdata(u32 d, u32 b1, u32 b0)
>  
>  /* ====== General helper routines ===== */
>  
> +static void sba_peek_mchans(struct sba_device *sba)
> +{
> +	int mchan_idx;
> +
> +	for (mchan_idx = 0; mchan_idx < sba->mchans_count; mchan_idx++)
> +		mbox_client_peek_data(sba->mchans[mchan_idx]);
> +}
> +
>  static struct sba_request *sba_alloc_request(struct sba_device *sba)
>  {
>  	unsigned long flags;
> @@ -211,8 +219,17 @@ static struct sba_request *sba_alloc_request(struct sba_device *sba)
>  	if (req)
>  		list_move_tail(&req->node, &sba->reqs_alloc_list);
>  	spin_unlock_irqrestore(&sba->reqs_lock, flags);
> -	if (!req)
> +
> +	if (!req) {
> +		/*
> +		 * We have no more free requests so, we peek
> +		 * mailbox channels hoping few active requests
> +		 * would have completed which will create more
> +		 * room for new requests.
> +		 */
> +		sba_peek_mchans(sba);
>  		return NULL;
> +	}
>  
>  	req->flags = SBA_REQUEST_STATE_ALLOCED;
>  	req->first = req;
> @@ -560,17 +577,15 @@ static enum dma_status sba_tx_status(struct dma_chan *dchan,
>  				     dma_cookie_t cookie,
>  				     struct dma_tx_state *txstate)
>  {
> -	int mchan_idx;
>  	enum dma_status ret;
>  	struct sba_device *sba = to_sba_device(dchan);
>  
> -	for (mchan_idx = 0; mchan_idx < sba->mchans_count; mchan_idx++)
> -		mbox_client_peek_data(sba->mchans[mchan_idx]);
> -
>  	ret = dma_cookie_status(dchan, cookie, txstate);
>  	if (ret == DMA_COMPLETE)
>  		return ret;
>  
> +	sba_peek_mchans(sba);

why do you want to do this while checking status..?

-- 
~Vinod