linux-kernel - Re: [PATCH RESEND v3 5/6] AHCI: Optimize single IRQ interrupt processing

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Message-ID: <20140923205710.GB17332@mtj.dyndns.org>
Date:	Tue, 23 Sep 2014 16:57:10 -0400
From:	Tejun Heo <tj@...nel.org>
To:	Alexander Gordeev <agordeev@...hat.com>
Cc:	linux-kernel@...r.kernel.org, linux-ide@...r.kernel.org
Subject: Re: [PATCH RESEND v3 5/6] AHCI: Optimize single IRQ interrupt
 processing

Hello, Alexander.

On Sun, Sep 21, 2014 at 03:19:28PM +0200, Alexander Gordeev wrote:
> Split interrupt service routine into hardware context handler
> and threaded context handler. That allows to protect ports with
> individual locks rather than with a single host-wide lock and
> move port interrupts handling out of the hardware interrupt
> context.
> 
> Testing was done by transferring 8GB on two hard drives in
> parallel using command 'dd if=/dev/sd{a,b} of=/dev/null'. With
> lock_stat statistics I measured access times to ata_host::lock
> spinlock (since interrupt handler code is fully embraced with
> this lock). The average lock's holdtime decreased eight times
> while average waittime decreased two times.
> 
> Both before and after the change the transfer time is the same,
> while 'perf record -e cycles:k ...' shows 1%-4% CPU time spent
> in ahci_single_irq_intr() routine before the update and not even
> sampled/shown ahci_single_irq_intr() after the update.

Hmmm... how does it affect single device operation tho?  It does make
individual interrupt handling heavier, no?

Thanks.

-- 
tejun
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