> On Nov 17, 2018, at 4:05 PM, Kyle Larose <[email protected]> wrote:
>
> On Sat, Nov 17, 2018 at 5:22 AM Harsh Patel <[email protected]> wrote:
>>
>> Hello,
>> Thanks a lot for going through the code and providing us with so much
>> information.
>> We removed all the memcpy/malloc from the data path as you suggested and
> ...
>> After removing this, we are able to see a performance gain but not as good
>> as raw socket.
>>
>
> You're using an unordered_map to map your buffer pointers back to the
> mbufs. While it may not do a memcpy all the time, It will likely end
> up doing a malloc arbitrarily when you insert or remove entries from
> the map. If it needs to resize the table, it'll be even worse. You may
> want to consider using librte_hash:
> https://doc.dpdk.org/api/rte__hash_8h.html instead. Or, even better,
> see if you can design the system to avoid needing to do a lookup like
> this. Can you return a handle with the mbuf pointer and the data
> together?
>
> You're also using floating point math where it's unnecessary (the
> timing check). Just multiply the numerator by 1000000 prior to doing
> the division. I doubt you'll overflow a uint64_t with that. It's not
> as efficient as integer math, though I'm not sure offhand it'd cause a
> major perf problem.
>
> One final thing: using a raw socket, the kernel will take over
> transmitting and receiving to the NIC itself. that means it is free to
> use multiple CPUs for the rx and tx. I notice that you only have one
> rx/tx queue, meaning at most one CPU can send and receive packets.
> When running your performance test with the raw socket, you may want
> to see how busy the system is doing packet sends and receives. Is it
> using more than one CPU's worth of processing? Is it using less, but
> when combined with your main application's usage, the overall system
> is still using more than one?
Along with the floating point math, I would remove all floating point math and
use the rte_rdtsc() function to use cycles. Using something like:
uint64_t cur_tsc, next_tsc, timo = (rte_timer_get_hz() / 16); /* One 16th of
a second use 2/4/8/16/32 power of two numbers to make the math simple divide */
cur_tsc = rte_rdtsc();
next_tsc = cur_tsc + timo; /* Now next_tsc the next time to flush */
while(1) {
cur_tsc = rte_rdtsc();
if (cur_tsc >= next_tsc) {
flush();
next_tsc += timo;
}
/* Do other stuff */
}
For the m_bufPktMap I would use the rte_hash or do not use a hash at all by
grabbing the buffer address and subtract the
mbuf = (struct rte_mbuf *)RTE_PTR_SUB(buf, sizeof(struct rte_mbuf) +
RTE_MAX_HEADROOM);
DpdkNetDevice:Write(uint8_t *buffer, size_t length)
{
struct rte_mbuf *pkt;
uint64_t cur_tsc;
pkt = (struct rte_mbuf *)RTE_PTR_SUB(buffer, sizeof(struct rte_mbuf) +
RTE_MAX_HEADROOM);
/* No need to test pkt, but buffer maybe tested to make sure it is not
null above the math above */
pkt->pk_len = length;
pkt->data_len = length;
rte_eth_tx_buffer(m_portId, 0, m_txBuffer, pkt);
cur_tsc = rte_rdtsc();
/* next_tsc is a private variable */
if (cur_tsc >= next_tsc) {
rte_eth_tx_buffer_flush(m_portId, 0, m_txBuffer); /*
hardcoded the queue id, should be fixed */
next_tsc = cur_tsc + timo; /* timo is a fixed number of cycles
to wait */
}
return length;
}
DpdkNetDevice::Read()
{
struct rte_mbuf *pkt;
if (m_rxBuffer->length == 0) {
m_rxBuffer->next = 0;
m_rxBuffer->length = rte_eth_rx_burst(m_portId, 0,
m_rxBuffer->pmts, MAX_PKT_BURST);
if (m_rxBuffer->length == 0)
return std::make_pair(NULL, -1);
}
pkt = m_rxBuffer->pkts[m_rxBuffer->next++];
/* do not use rte_pktmbuf_read() as it does a copy for the complete
packet */
return std:make_pair(rte_pktmbuf_mtod(pkt, char *), pkt->pkt_len);
}
void
DpdkNetDevice::FreeBuf(uint8_t *buf)
{
struct rte_mbuf *pkt;
if (!buf)
return;
pkt = (struct rte_mbuf *)RTE_PKT_SUB(buf, sizeof(rte_mbuf) +
RTE_MAX_HEADROOM);
rte_pktmbuf_free(pkt);
}
When your code is done with the buffer, then convert the buffer address back to
a rte_mbuf pointer and call rte_pktmbuf_free(pkt); This should eliminate the
copy and floating point code. Converting my C code to C++ priceless :-)
Hopefully the buffer address passed is the original buffer address and has not
be adjusted.
Regards,
Keith
