> On Mar 27, 2019, at 4:51 AM, Kevin Traynor <ktray...@redhat.com> wrote:
>
> On 25/03/2019 19:13, Yongseok Koh wrote:
>> When replenishing mbufs on Rx, buffer address (mbuf->buf_addr) should be
>> loaded. non-x86 processors (mostly RISC such as ARM and Power) are more
>> vulnerable to load stall. For x86, reducing the number of instructions
>> seems to matter most.
>>
>> For x86, this is simply a load but for other architectures, it is
>> calculated from the address of mbuf structure by rte_mbuf_buf_addr()
>> without having to load the first cacheline of the mbuf.
>>
>
> Hi Yongseok,
>
>> Fixes: 12d468a62bc1 ("net/mlx5: fix instruction hotspot on replenishing Rx
>> buffer")
>
> A similar backport was just added into 18.11.1-RC2, should it be
> reverted? I'm not keen to put another fix for it in for 18.11.1 at this
> stage, I think it can be part of 18.11.2. WDYT?
I spoke with Kevin and we decided to drop the old fix.
I have also dropped it from 17.11.6-rc1.
This new fix will be merged to 18.11.2.
I'll merge it to 17.11.6 (or 17.11.7) if it is merged in the master.
thanks,
Yongseok
>> Cc: sta...@dpdk.org
>>
>> Signed-off-by: Yongseok Koh <ys...@mellanox.com>
>> ---
>> drivers/net/mlx5/mlx5_rxtx_vec.h | 14 +++++++++++++-
>> 1 file changed, 13 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/net/mlx5/mlx5_rxtx_vec.h
>> b/drivers/net/mlx5/mlx5_rxtx_vec.h
>> index 5df8e291e6..4220b08dd2 100644
>> --- a/drivers/net/mlx5/mlx5_rxtx_vec.h
>> +++ b/drivers/net/mlx5/mlx5_rxtx_vec.h
>> @@ -102,9 +102,21 @@ mlx5_rx_replenish_bulk_mbuf(struct mlx5_rxq_data *rxq,
>> uint16_t n)
>> return;
>> }
>> for (i = 0; i < n; ++i) {
>> - void *buf_addr = rte_mbuf_buf_addr(elts[i], rxq->mp);
>> + void *buf_addr;
>>
>> + /*
>> + * Load the virtual address for Rx WQE. non-x86 processors
>> + * (mostly RISC such as ARM and Power) are more vulnerable to
>> + * load stall. For x86, reducing the number of instructions
>> + * seems to matter most.
>> + */
>> +#ifdef RTE_ARCH_X86_64
>> + buf_addr = elts[i]->buf_addr;
>> + assert(buf_addr == rte_mbuf_buf_addr(elts[i], rxq->mp));
>> +#else
>> + buf_addr = rte_mbuf_buf_addr(elts[i], rxq->mp);
>> assert(buf_addr == elts[i]->buf_addr);
>> +#endif
>> wq[i].addr = rte_cpu_to_be_64((uintptr_t)buf_addr +
>> RTE_PKTMBUF_HEADROOM);
>> /* If there's only one MR, no need to replace LKey in WQE. */
>>
>
