linux-kernel - Re: Spinlock debugging

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Message-Id: <1157995492.23085.191.camel@localhost.localdomain>
Date:	Mon, 11 Sep 2006 18:24:52 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Andrew Bird <ajb@...eresystems.co.uk>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: Spinlock debugging

Ar Llu, 2006-09-11 am 17:38 +0100, ysgrifennodd Andrew Bird:
> Alan
> 	Yes, I have low_latency set for kernels lower than 2.6.17. I'm currently 
> testing using 2.6.15. When you mention 'write method for flow control' do you 
> mean for software XON/XOFF etc?

Yes

Basically in low_latency the following is valid


	driver receives bytes
		flush_to_ldisc
			ldisc calls driver write methods


That means if you have a shared lock for read/write you want to drop it
after you've bashed the hardware and before you flush_to_ldisc. Remember
the IRQ handler is not re-entrant so another IRQ of the same number
won't cause further I/O and out of order receives.

Alan

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