Hi Gregory,
On Mon, 20 Feb 2017 15:21:35 +0100 Gregory CLEMENT wrote:
> Hi Jisheng,
>
> On lun., févr. 20 2017, Jisheng Zhang <jszh...@marvell.com> wrote:
>
> > In hot code path such as mvneta_rx_swbm(), we access fields of rx_desc
> > and tx_desc. These DMA descs are allocated by dma_alloc_coherent, they
> > are uncacheable if the device isn't cache coherent, reading from
> > uncached memory is fairly slow.
> >
> > patch1 reuses the read out status to getting status field of rx_desc
> > again.
> >
> > patch2 avoids getting buf_phys_addr from rx_desc again in
> > mvneta_rx_hwbm by reusing the phys_addr variable.
> >
> > patch3 avoids reading from tx_desc as much as possible by store what
> > we need in local variable.
> >
> > We get the following performance data on Marvell BG4CT Platforms
> > (tested with iperf):
> >
> > before the patch:
> > sending 1GB in mvneta_tx()(disabled TSO) costs 793553760ns
> >
> > after the patch:
> > sending 1GB in mvneta_tx()(disabled TSO) costs 719953800ns
> >
> > we saved 9.2% time.
> >
> > patch4 uses cacheable memory to store the rx buffer DMA address.
> >
> > We get the following performance data on Marvell BG4CT Platforms
> > (tested with iperf):
> >
> > before the patch:
> > recving 1GB in mvneta_rx_swbm() costs 1492659600 ns
> >
> > after the patch:
> > recving 1GB in mvneta_rx_swbm() costs 1421565640 ns
>
> Could you explain who you get this number?
Thanks for your review.
The measurement is simple: record how much time we spent in mvneta_rx_swbm()
for receiving 1GB data, something as below:
mvneta_rx_swbm()
{
static u64 total_time;
u64 t1, t2;
static u64 count;
t1 = sched_clock();
...
if (rcvd_pkts) {
...
t2 = sched_clock() - t1;
total_time += t2;
count += rcvd_bytes;;
if (count >= 0x40000000) {
printk("!!!! %lld %lld\n", total_time, count);
total_time = 0;
count = 0;
}
...
}
>
> receiving 1GB in 1.42 second means having a bandwidth of
> 8/1.42=5.63 Gb/s, that means that you are using at least a 10Gb
> interface.
hmmm, we just measured the time spent in mvneta_rx_swbm(), so we can't solve
the bandwidth as 8/1.42, what do you think?
>
> When I used iperf I didn't have this kind of granularity:
> iperf -c 192.168.10.1 -n 1024M
> ------------------------------------------------------------
> Client connecting to 192.168.10.19, TCP port 5001
> TCP window size: 43.8 KByte (default)
> ------------------------------------------------------------
> [ 3] local 192.168.10.28 port 53086 connected with 192.168.10.1 port 5001
> [ ID] Interval Transfer Bandwidth
> [ 3] 0.0- 9.1 sec 1.00 GBytes 942 Mbits/sec
>
> Also without HWBM enabled (so with the same configuration of your test),
> I didn't noticed any improvement with the patch set applied. But at
>From bandwidth point of view, yes, there's no improvement. But from cpu
time/load point of view, I do see a trivial improvement. Could you also
did a simple test from your side to see whether we have similar improvement
data?
Thanks,
Jisheng
> least I didn't see any regression with or without HWBM.
>
> Gregory
>
> >
> > We saved 4.76% time.
> >
> > Basically, patch1 and patch4 do what Arnd mentioned in [1].
> >
> > Hi Arnd,
> >
> > I added "Suggested-by you" tag, I hope you don't mind ;)
> >
> > Thanks
> >
> > [1] https://www.spinics.net/lists/netdev/msg405889.html
> >
> > Since v2:
> > - add Gregory's ack to patch1
> > - only get rx buffer DMA address from cacheable memory for
> > mvneta_rx_swbm()
> > - add patch 2 to read rx_desc->buf_phys_addr once in mvneta_rx_hwbm()
> > - add patch 3 to avoid reading from tx_desc as much as possible
> >
> > Since v1:
> > - correct the performance data typo
> >
> >
> > Jisheng Zhang (4):
> > net: mvneta: avoid getting status from rx_desc as much as possible
> > net: mvneta: avoid getting buf_phys_addr from rx_desc again
> > net: mvneta: avoid reading from tx_desc as much as possible
> > net: mvneta: Use cacheable memory to store the rx buffer DMA address
> >
> > drivers/net/ethernet/marvell/mvneta.c | 80
> > +++++++++++++++++++----------------
> > 1 file changed, 43 insertions(+), 37 deletions(-)
> >
> > --
> > 2.11.0
> >
>
