Re: [linuxppc-release] [PATCH v3 4/4] fsl-dma: use spin_lock_bh to instead of spin_lock_irqsave

On Tue, Jul 17, 2012 at 12:23 PM, Liu Qiang-B32616 [off-list ref] wrote:

quoted

-----Original Message-----
From: Tabi Timur-B04825
Sent: Monday, July 16, 2012 10:25 PM
To: Liu Qiang-B32616
Cc: linux-crypto@vger.kernel.org; linuxppc-dev@lists.ozlabs.org; Vinod
Koul; herbert@gondor.hengli.com.au; Dan Williams; Li Yang-R58472;
davem@davemloft.net
Subject: Re: [linuxppc-release] [PATCH v3 4/4] fsl-dma: use spin_lock_bh
to instead of spin_lock_irqsave

Qiang Liu wrote:

quoted

Use spin_lock_bh to instead of spin_lock_irqsave for improving

performance.

You forgot to include the evidence that performance has improved, as well
as an explanation why it's okay to use spin_lock_bh, and why it's faster.
  I told you to respin the patch with that information in the patch
description.

I attached the test result in v3 0/4, performance is improved by 2%.
For my understanding, there is not any place to access descriptor lists
in fsl-dma interrupt service handler except its tasklet, spin_lock_bh()
is born for this. Interrupts will be turned off and context will be save in
irqsave, there is needless to use irqsave in our case. You can refer to the
implement of mv_xor.c or ioap-adma.c.
If you think my explanation is ok, I can add it in the patch.

Disabling bottom half is not faster than disabling the interrupt.  But
by using it we reduce the time when interrupt is disabled.  We can get
better real time performance in term of interrupt handling latency.

Leo