netdev - Re: [PATCH net-next 1/2] mlx4_en: Add PTP hardware clock

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Message-ID: <20131223184845.GA4922@netboy>
Date:	Mon, 23 Dec 2013 19:48:46 +0100
From:	Richard Cochran <richardcochran@...il.com>
To:	Hadar Hen Zion <hadarh@...lanox.com>
Cc:	Shawn Bohrer <shawn.bohrer@...il.com>,
	"David S. Miller" <davem@...emloft.net>,
	Or Gerlitz <ogerlitz@...lanox.com>,
	Amir Vadai <amirv@...lanox.com>, netdev@...r.kernel.org,
	tomk@...advisors.com, Shawn Bohrer <sbohrer@...advisors.com>
Subject: Re: [PATCH net-next 1/2] mlx4_en: Add PTP hardware clock

On Sun, Dec 22, 2013 at 03:13:12PM +0200, Hadar Hen Zion wrote:

> 2. Adding spin lock in the data path reduce performance by 15% when
> HW timestamping is enabled. I did some testing and replacing
> spin_lock_irqsave with read/write_lock_irqsave prevents the
> performance decrease.

Why do the spin locks cause such a bottleneck?

Is there really that much lock contention in your test?

Your figure of 15% seems awfully high. How did you arrive at that
figure?

Thanks,
Richard
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