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From: Arnd Bergmann <arnd@arndb.de>
To: Tina Ruchandani <ruchandani.tina@gmail.com>
Cc: y2038@lists.linaro.org, linux-kernel@vger.kernel.org,
	dri-devel@lists.freedesktop.org,
	Thierry Reding <treding@nvidia.com>
Subject: Re: [PATCH v2] drm/msm: Use 64-bit timekeeping
Date: Sun, 17 Apr 2016 01:47:24 +0200	[thread overview]
Message-ID: <4683452.tNFHTvCUEu@wuerfel> (raw)
In-Reply-To: <20160413095214.GA101605@localhost>

On Wednesday 13 April 2016 02:52:14 Tina Ruchandani wrote:
>                         ktime_t rem = ktime_sub(*timeout, now);
> -                       struct timespec ts = ktime_to_timespec(rem);
> -                       remaining_jiffies = timespec_to_jiffies(&ts);
> +                       struct timespec64 ts = ktime_to_timespec64(rem);
> +
> +                       remaining_jiffies = timespec64_to_jiffies(&ts);
> 

Hi Tina,

The change looks correct to me, but I wonder if we should optimize
this code a little more, as it does two expensive 64-bit divisions.

How about

	remaining_jiffies = msecs_to_jiffies(ktime_ms_delta(*timeout, now));

which only does one 64-bit division, and it's one that we can probably
optimize out in the future (we can check in ktime_ms_delta whether the
difference is more than 2^32 nanoseconds as the fast path).

	Arnd
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WARNING: multiple messages have this Message-ID (diff)
From: Arnd Bergmann <arnd@arndb.de>
To: Tina Ruchandani <ruchandani.tina@gmail.com>
Cc: y2038@lists.linaro.org, dri-devel@lists.freedesktop.org,
	linux-kernel@vger.kernel.org, Wentao Xu <wentaox@codeaurora.org>,
	Thierry Reding <treding@nvidia.com>, Hai Li <hali@codeaurora.org>
Subject: Re: [PATCH v2] drm/msm: Use 64-bit timekeeping
Date: Sun, 17 Apr 2016 01:47:24 +0200	[thread overview]
Message-ID: <4683452.tNFHTvCUEu@wuerfel> (raw)
In-Reply-To: <20160413095214.GA101605@localhost>

On Wednesday 13 April 2016 02:52:14 Tina Ruchandani wrote:
>                         ktime_t rem = ktime_sub(*timeout, now);
> -                       struct timespec ts = ktime_to_timespec(rem);
> -                       remaining_jiffies = timespec_to_jiffies(&ts);
> +                       struct timespec64 ts = ktime_to_timespec64(rem);
> +
> +                       remaining_jiffies = timespec64_to_jiffies(&ts);
> 

Hi Tina,

The change looks correct to me, but I wonder if we should optimize
this code a little more, as it does two expensive 64-bit divisions.

How about

	remaining_jiffies = msecs_to_jiffies(ktime_ms_delta(*timeout, now));

which only does one 64-bit division, and it's one that we can probably
optimize out in the future (we can check in ktime_ms_delta whether the
difference is more than 2^32 nanoseconds as the fast path).

	Arnd

  reply	other threads:[~2016-04-16 23:47 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-04-13  9:52 [PATCH v2] drm/msm: Use 64-bit timekeeping Tina Ruchandani
2016-04-13  9:52 ` Tina Ruchandani
2016-04-16 23:47 ` Arnd Bergmann [this message]
2016-04-16 23:47   ` Arnd Bergmann
2016-04-21 11:35   ` Tina Ruchandani
2016-04-21 11:39     ` Tina Ruchandani
2016-04-21 11:39       ` Tina Ruchandani
2016-04-21 12:21       ` Arnd Bergmann
2016-04-21 12:21         ` Arnd Bergmann

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