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Message-ID: <4AC3E3C5.1090108@gmail.com>
Date: Thu, 01 Oct 2009 01:03:33 +0200
From: Eric Dumazet <eric.dumazet@...il.com>
To: Stephen Hemminger <shemminger@...tta.com>
CC: Jesper Dangaard Brouer <jdb@...x.dk>,
Robert Olsson <robert@...julf.net>, netdev@...r.kernel.org,
"David S. Miller" <davem@...emloft.net>
Subject: [PATCH] pktgen: Avoid dirtying skb->users when txq is full
Stephen Hemminger a écrit :
> On Tue, 22 Sep 2009 22:49:02 -0700
> Stephen Hemminger <shemminger@...tta.com> wrote:
>
>> I thought others want to know how to get maximum speed of pktgen.
>>
>> 1. Run nothing else (even X11), just a command line
>> 2. Make sure ethernet flow control is disabled
>> ethtool -A eth0 autoneg off rx off tx off
>> 3. Make sure clocksource is TSC. On my old SMP Opteron's
>> needed to get patch since in 2.6.30 or later, the clock guru's
>> decided to remove it on all non Intel machines. Look for patch
>> than enables "tsc=reliable"
>> 4. Compile Ethernet drivers in, the overhead of the indirect
>> function call required for modules (or cache footprint),
>> slows things down.
>> 5. Increase transmit ring size to 1000
>> ethtool -G eth0 tx 1000
>>
Thanks a lot Stephen.
I did some pktgen session tonight and found one contention on skb->users field
that following patch avoids.
Before patch :
------------------------------------------------------------------------------
PerfTop: 5187 irqs/sec kernel:100.0% [100000 cycles], (all, cpu: 0)
------------------------------------------------------------------------------
samples pcnt kernel function
_______ _____ _______________
16688.00 - 50.9% : consume_skb
6541.00 - 20.0% : skb_dma_unmap
3277.00 - 10.0% : tg3_poll
1968.00 - 6.0% : mwait_idle
651.00 - 2.0% : irq_entries_start
466.00 - 1.4% : _spin_lock
442.00 - 1.3% : mix_pool_bytes_extract
373.00 - 1.1% : tg3_msi
353.00 - 1.1% : read_tsc
177.00 - 0.5% : sched_clock_local
176.00 - 0.5% : sched_clock
137.00 - 0.4% : tick_nohz_stop_sched_tick
After patch:
------------------------------------------------------------------------------
PerfTop: 3530 irqs/sec kernel:99.9% [100000 cycles], (all, cpu: 0)
------------------------------------------------------------------------------
samples pcnt kernel function
_______ _____ _______________
17127.00 - 34.0% : tg3_poll
12691.00 - 25.2% : consume_skb
5299.00 - 10.5% : skb_dma_unmap
4179.00 - 8.3% : mwait_idle
1583.00 - 3.1% : irq_entries_start
1288.00 - 2.6% : mix_pool_bytes_extract
1239.00 - 2.5% : tg3_msi
1062.00 - 2.1% : read_tsc
583.00 - 1.2% : _spin_lock
432.00 - 0.9% : sched_clock
416.00 - 0.8% : sched_clock_local
360.00 - 0.7% : tick_nohz_stop_sched_tick
329.00 - 0.7% : ktime_get
263.00 - 0.5% : _spin_lock_irqsave
I believe we could go further, batching the atomic_inc(&skb->users) we do all the
time, competing with the atomic_dec() done by tx completion handler (possibly run
on other cpu): Reserve XXXXXXX units to the skb->users, and decrement a pktgen
local variable and refill the reserve if necessary, once in a while...
[PATCH] pktgen: Avoid dirtying skb->users when txq is full
We can avoid two atomic ops on skb->users if packet is not going to be
sent to the device (because hardware txqueue is full)
Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>
---
diff --git a/net/core/pktgen.c b/net/core/pktgen.c
index 4d11c28..6a9ab28 100644
--- a/net/core/pktgen.c
+++ b/net/core/pktgen.c
@@ -3439,12 +3439,14 @@ static void pktgen_xmit(struct pktgen_dev *pkt_dev)
txq = netdev_get_tx_queue(odev, queue_map);
__netif_tx_lock_bh(txq);
- atomic_inc(&(pkt_dev->skb->users));
- if (unlikely(netif_tx_queue_stopped(txq) || netif_tx_queue_frozen(txq)))
+ if (unlikely(netif_tx_queue_stopped(txq) || netif_tx_queue_frozen(txq))) {
ret = NETDEV_TX_BUSY;
- else
- ret = (*xmit)(pkt_dev->skb, odev);
+ pkt_dev->last_ok = 0;
+ goto unlock;
+ }
+ atomic_inc(&(pkt_dev->skb->users));
+ ret = (*xmit)(pkt_dev->skb, odev);
switch (ret) {
case NETDEV_TX_OK:
@@ -3466,6 +3468,7 @@ static void pktgen_xmit(struct pktgen_dev *pkt_dev)
atomic_dec(&(pkt_dev->skb->users));
pkt_dev->last_ok = 0;
}
+unlock:
__netif_tx_unlock_bh(txq);
/* If pkt_dev->count is zero, then run forever */
--
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