linux-kernel - Re: [PATCH 06/13] net: mvneta: enable mixed egress processing using HR timer

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Date:	Wed, 2 Dec 2015 11:03:56 +0100
From:	Marcin Wojtas <mw@...ihalf.com>
To:	Simon Guinot <simon.guinot@...uanux.org>
Cc:	linux-kernel@...r.kernel.org,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>, netdev@...r.kernel.org,
	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
	Andrew Lunn <andrew@...n.ch>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	Jason Cooper <jason@...edaemon.net>,
	Yair Mahalalel <myair@...vell.com>,
	Grzegorz Jaszczyk <jaz@...ihalf.com>,
	Evan Wang <xswang@...vell.com>, nadavh@...vell.com,
	Lior Amsalem <alior@...vell.com>,
	Tomasz Nowicki <tn@...ihalf.com>,
	Gregory Clément 
	<gregory.clement@...e-electrons.com>, nitroshift@...oo.com,
	"David S. Miller" <davem@...emloft.net>,
	Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>
Subject: Re: [PATCH 06/13] net: mvneta: enable mixed egress processing using
 HR timer

Hi Simon,

I checked using hrtimer_is_queued instead of a custom flag and it
resulted in ~20kpps drop in my setup. timer_scheduled flag is cleared
in the tasklet, so no timer can be scheduled until the tasklet is
executed. hr_timer flags do not cover this situation, so much more
timers are enqueued. I added a counter and with maximal throughput
during 30s test and 9 times less timers were enqueued with
timer_scheduled flag (~31k vs ~281k), so it's much more efficient and
I'll leave it as is.

Best regards,
Marcin

2015-11-30 16:57 GMT+01:00 Marcin Wojtas <mw@...ihalf.com>:
> Hi Simon,
>
> 2015-11-26 17:45 GMT+01:00 Simon Guinot <simon.guinot@...uanux.org>:
>> Hi Marcin,
>>
>> On Sun, Nov 22, 2015 at 08:53:52AM +0100, Marcin Wojtas wrote:
>>> Mixed approach allows using higher interrupt threshold (increased back to
>>> 15 packets), useful in high throughput. In case of small amount of data
>>> or very short TX queues HR timer ensures releasing buffers with small
>>> latency.
>>>
>>> Along with existing tx_done processing by coalescing interrupts this
>>> commit enables triggering HR timer each time the packets are sent.
>>> Time threshold can also be configured, using ethtool.
>>>
>>> Signed-off-by: Marcin Wojtas <mw@...ihalf.com>
>>> Signed-off-by: Simon Guinot <simon.guinot@...uanux.org>
>>> ---
>>>  drivers/net/ethernet/marvell/mvneta.c | 89 +++++++++++++++++++++++++++++++++--
>>>  1 file changed, 85 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/drivers/net/ethernet/marvell/mvneta.c b/drivers/net/ethernet/marvell/mvneta.c
>>> index 9c9e858..f5acaf6 100644
>>> --- a/drivers/net/ethernet/marvell/mvneta.c
>>> +++ b/drivers/net/ethernet/marvell/mvneta.c
>>> @@ -21,6 +21,8 @@
>>>  #include <linux/module.h>
>>>  #include <linux/interrupt.h>
>>>  #include <linux/if_vlan.h>
>>> +#include <linux/hrtimer.h>
>>> +#include <linux/ktime.h>
>>
>> ktime.h is already included by hrtimer.h.
>>
>>>  #include <net/ip.h>
>>>  #include <net/ipv6.h>
>>>  #include <linux/io.h>
>>> @@ -226,7 +228,8 @@
>>>  /* Various constants */
>>>
>>>  /* Coalescing */
>>> -#define MVNETA_TXDONE_COAL_PKTS              1
>>> +#define MVNETA_TXDONE_COAL_PKTS              15
>>> +#define MVNETA_TXDONE_COAL_USEC              100
>>
>> Maybe we should keep the default configuration and let the user choose
>> to enable (or not) this feature ?
>
> I think that this feature should be enabled by default, same as in RX
> (which is enabled by HW in ingress). It satisfies all kinds of traffic
> or queues sizes. I'd prefer a situation that if someone really wants
> to disable it (even if I don't know the possible justification), then
> let him use ethtool for this purpose.
>
>>
>>>  #define MVNETA_RX_COAL_PKTS          32
>>>  #define MVNETA_RX_COAL_USEC          100
>>>
>>> @@ -356,6 +359,11 @@ struct mvneta_port {
>>>       struct net_device *dev;
>>>       struct notifier_block cpu_notifier;
>>>
>>> +     /* Egress finalization */
>>> +     struct tasklet_struct tx_done_tasklet;
>>> +     struct hrtimer tx_done_timer;
>>> +     bool timer_scheduled;
>>
>> I think we could use hrtimer_is_queued() instead of introducing a new
>> variable.
>>
>
> Good point, i'll try that.
>
> Best regards,
> Marcin
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