Re: [Xen-devel] [PATCH 1/3] spinlock: use local_irq_disable() instead of local_irq_save() where possible

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Fri, Jan 09, 2015 at 04:09:30PM +0000, Andrew Cooper wrote:
> On 09/01/15 16:02, Konrad Rzeszutek Wilk wrote:
> > On Thu, Jan 08, 2015 at 04:13:03PM +0000, Jan Beulich wrote:
> >> ... as generally being a cheaper operation.
> > I was wondering if it would be possible to change some of the
> > EFLAGS after when we go in the 'cpu_relax' - and an interrupt
> > happens, we process it, alter the EFLAGS, then when we are
> > done, the EFLAGS are different - which the original code would
> > save when it was done sitting on the cpu_relax() loop.
> >
> > Actually that sounds bad - we only want to restore the flags
> > that we had when going in this spin lock. Would make sense
> > to add an ASSERT to check for flags being different from the
> > EFLAGS?
> 
> local_irq_restore() only restores the interrupt flag from flags.  All
> other bits in EFLAGS are unmodified.

which I would have found out if I read the code from local_irq_restore().

Sorry about the noise - should have looked at the code before asking
questions!
> 
> ~Andrew

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