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SubjectRe: [PATCH tip/core/rcu 0/4] Programmatic nestable expedited grace periods
On 2/20/2015 9:43 AM, Peter Zijlstra wrote:
> On Fri, Feb 20, 2015 at 09:32:39AM -0800, Arjan van de Ven wrote:
>> there's a few others as well that I'm chasing down...
>> .. but the flip side, prior to running ring 3 code, why NOT do fast expedites?
>
> So my objections are twofold:
>
> - I object to fast expedites in principle; they spray IPIs across the
> system, so ideally we'd not have them at all, therefore also not at
> boot.
>
> Because as soon as the option exists, people will use it for other
> things too.

the option exists today in sysfs and kernel parameter...
>
> And esp. in bootup code you can special case a lot of stuff; there's
> limited concurrency esp. because userspace it not there yet. So we might
> not actually need those sync calls.

yeah I am going down that angle as well absolutely.
but there are cases that may well be legit (or are 5 function calls deep into common code)



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