On 8/21/25 3:02 PM, Mingming Cao wrote: > POWER8 support a maximum of 16 subcrq indirect descriptor entries per > H_SEND_SUB_CRQ_INDIRECT call, while POWER9 and newer hypervisors > support up to 128 entries. Increasing the max number of indirect > descriptor entries improves batching efficiency and reduces > hcall overhead, which enhances throughput under large workload on POWER9+. > > Currently, ibmvnic driver always uses a fixed number of max indirect > descriptor entries (16). send_subcrq_indirect() treats all hypervisor > errors the same: > - Cleanup and Drop the entire batch of descriptors. > - Return an error to the caller. > - Rely on TCP/IP retransmissions to recover. > - If the hypervisor returns H_PARAMETER (e.g., because 128 > entries are not supported on POWER8), the driver will continue > to drop batches, resulting in unnecessary packet loss. > > In this patch: > Raise the default maximum indirect entries to 128 to improve ibmvnic > batching on morden platform. But also gracefully fall back to > 16 entries for Power 8 systems. > > Since there is no VIO interface to query the hypervisor’s supported > limit, vnic handles send_subcrq_indirect() H_PARAMETER errors: > - On first H_PARAMETER failure, log the failure context > - Reduce max_indirect_entries to 16 and allow the single batch to drop. > - Subsequent calls automatically use the correct lower limit, > avoiding repeated drops. > > The goal is to optimizes performance on modern systems while handles > falling back for older POWER8 hypervisors. > > Performance shows 40% improvements with MTU (1500) on largework load. > > Signed-off-by: Mingming Cao <m...@linux.ibm.com> > Reviewed-by: Brian King <bjki...@linux.ibm.com> > Reviewed-by: Haren Myneni <ha...@linux.ibm.com> > Reviewed-by: Simon Horman <ho...@kernel.org> > -------------------------------------- > Changes since v3: > Link to v3: https://www.spinics.net/lists/netdev/msg1112828.html
For future memory: please use lore links instead. Thanks, Paolo
