Re: [dpdk-dev] add support for HTM lock elision for x86

[Roman Dementiev <roman.dementiev@intel.com>]

Hello Stephen,

Wednesday, June 3, 2015, 8:40:14 PM, you wrote:

> On Tue,  2 Jun 2015 15:11:30 +0200
> Roman Dementiev <roman.dementiev@intel.com> wrote:

>> 
>> This series of patches adds methods that use hardware memory transactions (HTM)
>> on fast-path for DPDK locks (a.k.a. lock elision). Here the methods are implemented 
>> for x86 using Restricted Transactional Memory instructions (Intel(r) Transactional 
>> Synchronization Extensions). The implementation fall-backs to the normal DPDK lock
>> if HTM is not available or memory transactions fail.
>> This is not a replacement for all lock usages since not all critical sections protected
>> by locks are friendly to HTM.
>> 


> You probably want to put a caveat around this, it won't work for people
> that expect to use spinlocks to protect I/O operations on hardware.
> Since I/O operations aren't like memory.

yes, I/O  can not  be  rolled  back by the CPU if the transaction should fail. Thus
the  HTM  transaction  protecting I/O operations are always aborted by
CPU. In Intel TSX the I/O operations (MMIO, outp, etc) are TSX-unfriendly
causing immediate abort.

-- 
Best regards,
 Roman                            mailto:roman.dementiev@intel.com

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