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John Plevyak commented on TS-1742: ---------------------------------- There are still a number of volatile declarations associated head_p, and they need to be made consistent. Anyone with an ARM/i386 system want to do the honors? At the very least it looks like here and in ink_queue.h where head_p itself is declared volatile. john > Freelists to use 64bit version w/ Double Word Compare and Swap > -------------------------------------------------------------- > > Key: TS-1742 > URL: https://issues.apache.org/jira/browse/TS-1742 > Project: Traffic Server > Issue Type: Improvement > Reporter: Brian Geffon > Assignee: Brian Geffon > Fix For: 3.3.2 > > Attachments: 128bit_cas.patch, 128bit_cas.patch.2 > > > So to those of you familiar with the freelists you know that it works this > way the head pointer uses the upper 16 bits for a version to prevent the ABA > problem. The big drawback to this is that it requires the following macros to > get at the pointer or the version: > {code} > #define FREELIST_POINTER(_x) ((void*)(((((intptr_t)(_x).data)<<16)>>16) | \ > (((~((((intptr_t)(_x).data)<<16>>63)-1))>>48)<<48))) // sign extend > #define FREELIST_VERSION(_x) (((intptr_t)(_x).data)>>48) > #define SET_FREELIST_POINTER_VERSION(_x,_p,_v) \ > (_x).data = ((((intptr_t)(_p))&0x0000FFFFFFFFFFFFULL) | (((_v)&0xFFFFULL) > << 48)) > {code} > Additionally, since this only leaves 16 bits it limits the number of versions > you can have, well more and more x86_64 processors support DCAS (double word > compare and swap / 128bit CAS). This means that we can use 64bits for a > version which basically makes the versions unlimited but more importantly it > takes those macros above and simplifies them to: > {code} > #define FREELIST_POINTER(_x) (_x).s.pointer > #define FREELIST_VERSION(_x) (_x).s.version > #define SET_FREELIST_POINTER_VERSION(_x,_p,_v) \ > (_x).s.pointer = _p; (_x).s.version = _v > {code} > As you can imagine this will have a performance improvement, in my simple > tests I measured a performance improvement of around 6%. Unfortunately, I'm > not an expert with this stuff and I would really appreciate more community > feedback before I commit this patch. > Note: this only applies if you're not using a reclaimable freelist. -- This message is automatically generated by JIRA. If you think it was sent incorrectly, please contact your JIRA administrators For more information on JIRA, see: http://www.atlassian.com/software/jira