linux-kernel - Re: [PATCH for-next 1/4] dmaengine: ti: k3-udma: Use ktime/usleep

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Date:   Tue, 28 Jan 2020 18:14:03 +0530
From:   Vinod Koul <vkoul@...nel.org>
To:     Vignesh Raghavendra <vigneshr@...com>
Cc:     Peter Ujfalusi <peter.ujfalusi@...com>, dmaengine@...r.kernel.org,
        linux-kernel@...r.kernel.org, dan.j.williams@...el.com,
        grygorii.strashko@...com
Subject: Re: [PATCH for-next 1/4] dmaengine: ti: k3-udma: Use
 ktime/usleep_range based TX completion check

On 28-01-20, 17:35, Vignesh Raghavendra wrote:

> >> +	/* Transfer is incomplete, store current residue and time stamp */
> >>  	if (peer_bcnt < bcnt) {
> >>  		uc->tx_drain.residue = bcnt - peer_bcnt;
> >> -		uc->tx_drain.jiffie = jiffies;
> >> +		uc->tx_drain.tstamp = ktime_get();
> > 
> > Any reason why ktime_get() is better than jiffies..?
> 
> Resolution of jiffies is 4ms. ktime_t is has better resolution (upto ns
> scale). With jiffies, I observed that code was either always polling DMA
> progress counters (which affects HW data transfer speed) or sleeping too
> long, both causing performance loss. Switching to ktime_t provides
> better prediction of how long transfer takes to complete.

Thanks for explanation, i think it is good info to add in changelog.

-- 
~Vinod