RE: mempool cache change

["Morten Brørup" <mb@smartsharesystems.com>]

> From: fengchengwen [mailto:fengchengwen@huawei.com]
> Sent: Wednesday, 15 July 2026 10.12
> 
> On 7/15/2026 4:08 AM, Morten Brørup wrote:
> > Hi Kishore,
> >
> > For your testing purposes, please follow the guidance provided to
> Wisam Jaddo:
> >
> https://inbox.dpdk.org/dev/98CBD80474FA8B44BF855DF32C47DC35F65964@smart
> server.smartshare.dk/
> 
> We need to recompile in this case. We should try to avoid
> recompilation.
> I think it is necessary to adjust RTE_MEMPOOL_CACHE_MAX_SIZE to 768 as
> a default configuration.

Changing RTE_MEMPOOL_CACHE_MAX_SIZE breaks both the API and the ABI; so it has to be done when building locally, where API/ABI breakage is acceptable.

For DPDK 26.11, where API/ABI breakage is acceptable, we can discuss increasing the default from 512 to a higher value. I do have some input to that discussion, but let's postpone it until after DPDK 26.07 has been released.

> 
> Thanks
> 
> >
> > Thank you for testing!
> >
> > Venlig hilsen / Kind regards,
> > -Morten Brørup
> >
> > From: Kishore Padmanabha [mailto:kishore.padmanabha@broadcom.com]
> > Sent: Tuesday, 14 July 2026 18.49
> > To: Thomas Monjalon; Morten Brørup
> > Cc: dev@dpdk.org
> > Subject: mempool cache change
> >
> > Hi Thomas,
> >
> > The recent change done as part of BUG ID: 1027, with commit id
> https://git.dpdk.org/dpdk/commit/?id=f5e1310f16e0909e7e7f71807123644c63
> b23cba
> > Is causing performance drop for the bnxt NIC in 26.07 release.
> >
> > The smaller, shallower cache increases the miss rate, causing refills
> to hit the shared ring more frequently.
> > In the old code, the cache only touched the shared ring when it
> climbed past 768 instead of 512. That extra 256 elements of headroom
> allowed significantly more frees to remain local.
> >
> > Could we make the change in config/rte_config.h for
> RTE_MEMPOOL_CACHE_MAX_SIZE to be 768 instead of 512. Since we use –
> mbcache=512 as argument for the performance tests.
> >
> > Thanks,
> > Kishore
> >
> >