Could it be meaningful to request that the whole buffer pool or other shared memory area has a minimum alignment? E.g. to enable or simplify huge pages TLB mapping? Is this what you are alluding to Petri here with shm align?
Regarding TLB page sizes and alignment, we shouldn't be too focused on 4KB. Many architectures support larger pages sizes (e.g. 16KB or 64KB) also for normal TLB entries. On 9 December 2014 at 15:11, Savolainen, Petri (NSN - FI/Espoo) <[email protected]> wrote: > Requirement for shm align maybe larger than 4KB (e.g. some number of > MBytes). Another config for that ODP_CONFIG_SHM_ALIGN_MAX ? > > > > -Petri > > > > > > > > From: ext Bill Fischofer [mailto:[email protected]] > Sent: Tuesday, December 09, 2014 3:07 PM > To: Savolainen, Petri (NSN - FI/Espoo) > Cc: lng-odp-forward > Subject: Re: [lng-odp] Alignment question > > > > The APIs that currently support alignment are odp_buffer_pool_create() and > odp_shm_reserve() > > > > On Tue, Dec 9, 2014 at 7:03 AM, Bill Fischofer <[email protected]> > wrote: > > That makes sense. I'll add those additional CONFIG vars to the v3 patch. I > don't see a use case for alignments above 4K for RAW buffers so that's a > reasonable upper limit, however I suspect some implementations may have > problems with that. If a platform has a HW buffer manager that uses 512 > byte blocks, they are going to be 512-byte aligned and it's meaningless to > try to ask for a higher alignment. > > > > On Tue, Dec 9, 2014 at 6:54 AM, Savolainen, Petri (NSN - FI/Espoo) > <[email protected]> wrote: > > > > > > From: [email protected] > [mailto:[email protected]] On Behalf Of ext Bill Fischofer > Sent: Tuesday, December 09, 2014 1:08 PM > To: lng-odp-forward > Subject: [lng-odp] Alignment question > > > > A number of APIs support a buf_align parameter but we haven't been terribly > precise about limits on this, so some questions for Petri. > > > > I think only buffer_pool_create has alignment parameter. > > > > With buf_align being defined as uint32_t in theory we can specify alignments > up to 2GB. > > > > 1. MAY implementations impose a lower upper limit on the alignments they > support? > > > > ODP_CONFIG_BUFFER_ALIGN_MAX (4*1024) ? > > > > > > 2. If so, what is the minimum acceptable upper alignment limit? We've > specified that buffers MUST be at minimum 8 byte aligned but is that > sufficient? > > > > ODP_CONFIG_BUFFER_ALIGN_MIN 8 ? > > > > 3. If implementations MAY impose an upper alignment limit below 2GB, what > SHOULD happen if an application requests an alignment above this limit? > Fail the request? Saturate at the implementation-defined max alignment? > > > > It should fail. User requests minimum alignment, implementation can round > up. > > > > -Petri > > > > > > > > > _______________________________________________ > lng-odp mailing list > [email protected] > http://lists.linaro.org/mailman/listinfo/lng-odp > _______________________________________________ lng-odp mailing list [email protected] http://lists.linaro.org/mailman/listinfo/lng-odp
