[Varnish] #665: should provide function for aligned allocations on the workspace

[Varnish]

#665: should provide function for aligned allocations on the workspace
-------------------------+--------------------------------------------------
 Reporter:  slink        |       Owner:  phk                                    
     Type:  enhancement  |      Status:  new                                    
 Priority:  normal       |   Milestone:                                         
Component:  varnishd     |     Version:  trunk                                  
 Severity:  normal       |    Keywords:  ws_alloc workspace allocation alignment
-------------------------+--------------------------------------------------
 When WS_Malloc was implemented, it was probably designed for the purpose
 of allocating memory for strings only, but it is now being used for
 allocation of space for arbitrary data structures. In general, such
 allocations may have alignment requirements.

 While alignment is enforced only on some harware platforms (many of which
 have become less popular (such as SPARC (unfortunetely) or MIPS)), also
 AMD makes a clear recommendation for the popular AMD64 platform:

 http://www.amd.com/us-
 en/assets/content_type/DownloadableAssets/dwamd_AMD64_Porting_FAQ.pdf

   What are the memory alignment requirements for code and data in
   each of these operating systems?

   There are no alignment requirements. x86 architecture has never had any
 alignment requirements and the 64-bit extensions have not added any.
 However, the ABI for 64-bit software has been designed to improve
 performance by striving for natural alignment of most memory operands.
 Natural alignment means that 2-byte objects are stored on 2-byte
 boundaries, 4-byte objects on 4-byte boundaries, etc. The performance
 side-effects of poorly aligned operands can be large.

 or here: http://developer.amd.com/pages/11112003167.aspx

   [...] a misaligned memory access can require more bus cycles than an
 aligned access. For maximum performance, avoid misaligned memory accesses.

 Therefor I am suggesting to introduce WS_Malloc for generic pointer-size
 aligned allocations (and WS_Calloc as a convenience function while I was
 at it already).

-- 
Ticket URL: <http://www.varnish-cache.org/ticket/665>
Varnish <http://varnish.projects.linpro.no/>
The Varnish HTTP Accelerator