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Message-ID: <87sik6kfa8.fsf@rustcorp.com.au>
Date: Fri, 05 Sep 2014 11:19:19 +0930
From: Rusty Russell <rusty@...tcorp.com.au>
To: Jesper Dangaard Brouer <brouer@...hat.com>
Cc: netdev <netdev@...r.kernel.org>,
Mathias Krause <minipli@...glemail.com>, brouer@...hat.com,
Robert Olsson <robert@...julf.net>
Subject: Re: [PATCH] pktgen: nowait parameter.
Jesper Dangaard Brouer <brouer@...hat.com> writes:
> On Wed, 03 Sep 2014 13:50:01 +0930
> Rusty Russell <rusty@...tcorp.com.au> wrote:
>
>> While trying to measure speed of virtio_net, I was getting hangs.
>> This is because we skb_orphan() but delay the tx interrupt
>> indefinitely (by number of slots).
>>
>> With nowait, pktgen won't wait for the skb to be released. This
>> introduces an error, but it's ok if count >> ringsize.
>
> This pktgen_wait_for_skb() only happens it the exit case, when count
> packets have been send. I guess its okay to proceed to
> pktgen_stop_device() which will call kfree_skb(pkt_dev->skb) with
> refcnt=2, decrementing to refcnt=1, and then we depend on driver to
> eventually call kfree_skb().
Yes, exactly.
>> I updated the documentation, but it needs far more work (it
>> refers to pgset and an examples directory, none of which exist
>> in the kernel tree).
>
> Yes, the doc is not in such a good shape.
>
> I'm not 100% happy with the name "nowait" parameter, as users could
> easily misunderstand the purpose of this parameter. But I've not come
> up with a better name, e.g. "exit_nowait" is also not the best.
Agreed. It could also be a flag, though that doesn't help with the name.
> diff --git a/net/core/pktgen.c b/net/core/pktgen.c
>> index 8b849ddfef2e..adc41f2b3bc7 100644
>> --- a/net/core/pktgen.c
>> +++ b/net/core/pktgen.c
>> @@ -290,6 +290,11 @@ struct pktgen_dev {
>> * set clone_skb to 1024.
>> */
>>
>> + bool no_wait; /*
>> + * Don't wait for packet to be freed
>> + * by driver
>> + */
>> +
>
> DaveM prefers multi line comments like:
>
> /* Don't wait for packet to be freed
> * by driver
> */
He does, but the rest of the kernel and the comment immediately above
doesn't:
int clone_skb; /*
* Use multiple SKBs during packet gen.
* If this number is greater than 1, then
* that many copies of the same packet will be
* sent before a new packet is allocated.
* If you want to send 1024 identical packets
* before creating a new packet,
* set clone_skb to 1024.
*/
>> char dst_min[IP_NAME_SZ]; /* IP, ie 1.2.3.4 */
>> char dst_max[IP_NAME_SZ]; /* IP, ie 1.2.3.4 */
>> char src_min[IP_NAME_SZ]; /* IP, ie 1.2.3.4 */
>> @@ -679,6 +684,9 @@ static int pktgen_if_show(struct seq_file *seq, void *v)
>>
>> seq_puts(seq, "\n");
>>
>> + if (pkt_dev->no_wait)
>> + seq_puts(seq, " nowait\n");
>> +
>
> Shouldn't you put this print statement above the "Flags:" section?
Sure.
>> /* not really stopped, more like last-running-at */
>> stopped = pkt_dev->running ? ktime_get() : pkt_dev->stopped_at;
>> idle = pkt_dev->idle_acc;
>> @@ -1711,6 +1719,17 @@ static ssize_t pktgen_if_write(struct file *file,
Subject: pktgen: nowait parameter.
While trying to measure speed of virtio_net, I was getting hangs.
This is because we skb_orphan() but delay the tx interrupt
indefinitely (by number of slots).
With nowait, pktgen won't wait for the skb to be released. This
introduces an error, but it's ok if count >> ringsize.
I updated the documentation, but it needs far more work (it
refers to pgset and an examples directory, none of which exist
in the kernel tree).
Signed-off-by: Rusty Russell <rusty@...tcorp.com.au>
diff --git a/Documentation/networking/pktgen.txt b/Documentation/networking/pktgen.txt
index 0dffc6e37902..dbd993d1e7f8 100644
--- a/Documentation/networking/pktgen.txt
+++ b/Documentation/networking/pktgen.txt
@@ -41,10 +41,13 @@ NIC HW layer (which is bad for bufferbloat).
One should be careful to conclude, that packets/descriptors in the HW
TX ring cause delay. Drivers usually delay cleaning up the
ring-buffers (for various performance reasons), thus packets stalling
-the TX ring, might just be waiting for cleanup.
+the TX ring, might just be waiting for cleanup. Writing the "nowait"
+parameter into /proc/net/pktgen/ethX will avoid waiting for cleanup of
+the final packets, introducing a slight error (tiny if the count of
+packets being sent is much greater than the ring size of the device).
-This cleanup issues is specifically the case, for the driver ixgbe
-(Intel 82599 chip). This driver (ixgbe) combine TX+RX ring cleanups,
+Alternately, some drivers (eg ixgbe for the Intel 82599 chip) can
+have their cleanup interval changed. ixgbe combines TX+RX ring cleanups,
and the cleanup interval is affected by the ethtool --coalesce setting
of parameter "rx-usecs".
@@ -303,6 +306,8 @@ flowlen
rate
ratep
+nowait
+
References:
ftp://robur.slu.se/pub/Linux/net-development/pktgen-testing/
ftp://robur.slu.se/pub/Linux/net-development/pktgen-testing/examples/
diff --git a/net/core/pktgen.c b/net/core/pktgen.c
index 8b849ddfef2e..1589f5ac0509 100644
--- a/net/core/pktgen.c
+++ b/net/core/pktgen.c
@@ -290,6 +290,8 @@ struct pktgen_dev {
* set clone_skb to 1024.
*/
+ bool no_wait; /* Don't wait for packet to be freed by driver */
+
char dst_min[IP_NAME_SZ]; /* IP, ie 1.2.3.4 */
char dst_max[IP_NAME_SZ]; /* IP, ie 1.2.3.4 */
char src_min[IP_NAME_SZ]; /* IP, ie 1.2.3.4 */
@@ -615,6 +617,9 @@ static int pktgen_if_show(struct seq_file *seq, void *v)
if (pkt_dev->node >= 0)
seq_printf(seq, " node: %d\n", pkt_dev->node);
+ if (pkt_dev->no_wait)
+ seq_puts(seq, " nowait\n");
+
seq_puts(seq, " Flags: ");
if (pkt_dev->flags & F_IPV6)
@@ -1711,6 +1716,17 @@ static ssize_t pktgen_if_write(struct file *file,
return count;
}
+ if (!strcmp(name, "nowait")) {
+ len = num_arg(&user_buffer[i], 10, &value);
+ if (len < 0)
+ return len;
+
+ i += len;
+ pkt_dev->no_wait = value;
+ sprintf(pg_result, "OK: nowait=%u", pkt_dev->no_wait);
+ return count;
+ }
+
sprintf(pkt_dev->result, "No such parameter \"%s\"", name);
return -EINVAL;
}
@@ -3373,7 +3389,8 @@ unlock:
/* If pkt_dev->count is zero, then run forever */
if ((pkt_dev->count != 0) && (pkt_dev->sofar >= pkt_dev->count)) {
- pktgen_wait_for_skb(pkt_dev);
+ if (!pkt_dev->no_wait)
+ pktgen_wait_for_skb(pkt_dev);
/* Done with this */
pktgen_stop_device(pkt_dev);
@@ -3565,6 +3582,7 @@ static int pktgen_add_device(struct pktgen_thread *t, const char *ifname)
pkt_dev->svlan_cfi = 0;
pkt_dev->svlan_id = 0xffff;
pkt_dev->node = -1;
+ pkt_dev->no_wait = false;
err = pktgen_setup_dev(t->net, pkt_dev, ifname);
if (err)
--
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