[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH] x86/time: Adjust init-time handling of pit0_ticks
On 20/12/2016 07:25, Jan Beulich wrote: >>>> On 19.12.16 at 17:58, <andrew.cooper3@xxxxxxxxxx> wrote: >> On 19/12/16 16:51, Jan Beulich wrote: >>>>>> On 19.12.16 at 17:38, <andrew.cooper3@xxxxxxxxxx> wrote: >>>> There is no need for the volatile cast in the timer interrupt. pit0_ticks >>>> has >>>> external linkage, preventing the compiler from eliding the update. This >>>> reduces the generated assembly from a read, local modify, write to a single >>>> add instruction. >>> I don't think external linkage is the reason here, considering the >>> effects of whole-program-optimization. >> In the case of whole-program-optimisation, the compiler would observe >> that one function wrote to the variable, and one function read from it. >> I presume that is also sufficient to prevent the eliding? > I would think so, yes (albeit the end result of that process may > be that everything which isn't recursive and doesn't serve as > independent entry point ends up as a few huge functions); I > merely wanted to point out that linkage isn't really relevant here. What about this? There is no need for the volatile cast in the timer interrupt; the compiler may not elide the update. This reduces the generated assembly from a read, local modify, write to a single add instruction. ~Andrew _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx https://lists.xen.org/xen-devel
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