From: Nachi Prachanda <nprachan@Brocade.com>
To: "skhare@vmware.com" <skhare@vmware.com>
Cc: Chas Williams III <ciwillia@Brocade.com>, "dev@dpdk.org" <dev@dpdk.org>
Subject: Re: [dpdk-dev] [PATCH 1/6] net/vmxnet3: retain counters on restart
Date: Fri, 26 May 2017 19:01:42 +0000 [thread overview]
Message-ID: <4cac962ba2ef4a059e44d8884c8e7ea3@HQ1WP-EXMB12.corp.brocade.com> (raw)
In-Reply-To: <alpine.DEB.2.10.1705261027530.5989@shri-linux.eng.vmware.com>
> -----Original Message-----
> From: Shrikrishna Khare [mailto:skhare@shri-linux.eng.vmware.com]
> Sent: Friday, May 26, 2017 10:29 AM
> To: Nachi Prachanda
> Cc: skhare@vmware.com; Chas Williams III; dev@dpdk.org
> Subject: RE: [PATCH 1/6] net/vmxnet3: retain counters on restart
>
>
>
> On Thu, 25 May 2017, Nachi Prachanda wrote:
>
> > > From: Shrikrishna Khare [mailto:skhare@shri-linux.eng.vmware.com]
> > > Sent: Thursday, May 25, 2017 1:27 PM
> > >
> > > On Thu, 25 May 2017, Nachi Prachanda wrote:
> > >
> > > > > From: Shrikrishna Khare
> > > > > [mailto:skhare@shri-linux.eng.vmware.com]
> > > > > Sent: Wednesday, May 24, 2017 2:10 PM
> > > > >
> > > > > On Fri, 19 May 2017, Charles (Chas) Williams wrote:
> > > > >
> > > > > > From: Nachiketa Prachanda <nprachan@brocade.com>
> > > > > >
> > > > > > Most nics like virtio, igb/ixgbe etc. don't reset counters on
> > > > > > dev_start and arguably this helps in monitoring the counters
> > > > > > across a longer time span with multiple device start/stops.
> > > > > > vmxnet3 behavior is opposite to that and counters are reset by
> > > > > > the host side implementation each time the device is restarted.
> > > > > >
> > > > > > Change the driver to save the counters in its private context
> > > > > > before it is reset by writing CMD_ACTIVATE to REG_CMD.
> > > > > >
> > > > > > Signed-off-by: Nachiketa Prachanda <nprachan@brocade.com>
> > > > >
> > > > > This won't be able to deal with vMotion or suspend/resume?
> > > >
> > > > Correct - this can't deal with the VM suspend/resume unless
> > > > hypervisor
> > > maintains the counter. But this patch doesn't make that behavior any
> > > worse than what it was before.
> > >
> > > The current code always resets stats, but am concerned that this
> > > patch will make the behavior inconsistent for cases like suspend/resume.
> > >
> > > Wondering if this will be better handled by the device emulation
> > > instead of the driver (for igb/ixgbe, is this handled by the hardware?).
> >
> > A little more nuanced.. - see below.
> >
> > > If we were to handle this in the device emulation, what would be the
> > > goals/requirements:
> > > - device start/stop should not reset stats?
> > > - any other operations where we would like to maintain/reset stats?
> > > - what might be the expectation around how accurate the stats need to
> be?
> > > - any other requirement on the device?
> >
> > I haven't thought about dealing it at the emulation layer - but the
> > expectation would be not clear counters not cleared for the lifetime
> > of the device - and have a way to clear them from the driver when needed.
> >
> > don't know if there is a standard behavior about resetting counters.
> > But for igb/ixgb the counters are read/clear registers and they are
> > maintained at driver. May not be always accurate if the hardware is
> > reset without updating the driver's counter - but at least ensures
> > that it is monotonically increasing since on each read driver only gets the
> delta.
> >
> > virtio emulation doesn't provide the counters - mostly the
> > receive/send functions updates the counters.
> >
> > >
> > > Also, note that if we proceed with this patch, and later extend
> > > device support to not reset stats, driver with this patch running on
> > > the extended device will report incorrect stats.
> >
> > Agree - it will need some work if the emulation changes.
>
> I spent some time looking at the emulation code. It turns out that these stats
> are already retained across vMotion, suspend/resume. And we have no
> immediate plan to change the device behavior to retain these stats across
> device start/stop. So am fine with this patch. Thank you for being patient with
> this.
Thanks for checking this out.
Nachi
>
> Thanks,
> Shri
>
>
> >
> > Regards,
> > Nachi
> >
> > > Thanks,
> > > Shri
> >
next prev parent reply other threads:[~2017-05-26 19:01 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-05-19 17:55 Charles (Chas) Williams
2017-05-19 17:55 ` [dpdk-dev] [PATCH 2/6] net/vmxnet3: Implement retrieval of extended stats Charles (Chas) Williams
2017-05-24 0:17 ` Shrikrishna Khare
2017-05-19 17:55 ` [dpdk-dev] [PATCH 3/6] net/vmxnet3: Generate link-state change notifications Charles (Chas) Williams
2017-05-19 17:55 ` [dpdk-dev] [PATCH 4/6] net/vmxnet3: Make vmxnet3_process_events less noisy Charles (Chas) Williams
2017-05-23 21:44 ` Shrikrishna Khare
2017-05-19 17:55 ` [dpdk-dev] [PATCH 5/6] net/vmxnet3: receive queue lockup and memleak Charles (Chas) Williams
2017-06-01 12:24 ` Charles (Chas) Williams
2017-05-24 21:09 ` [dpdk-dev] [PATCH 1/6] net/vmxnet3: retain counters on restart Shrikrishna Khare
2017-05-25 18:31 ` Nachi Prachanda
2017-05-25 20:27 ` Shrikrishna Khare
2017-05-25 22:08 ` Nachi Prachanda
2017-05-26 17:29 ` Shrikrishna Khare
2017-05-26 19:01 ` Nachi Prachanda [this message]
2017-05-26 17:31 ` Shrikrishna Khare
2017-06-15 12:16 ` [dpdk-dev] [PATCH V2 0/6] some local vmxnet3 patches Charles (Chas) Williams
2017-06-15 12:16 ` [dpdk-dev] [PATCH v2 1/6] net/vmxnet3: retain counters on restart Charles (Chas) Williams
2017-06-15 12:16 ` [dpdk-dev] [PATCH v2 2/6] net/vmxnet3: Implement retrieval of extended stats Charles (Chas) Williams
2017-06-21 1:42 ` Shrikrishna Khare
2017-06-15 12:16 ` [dpdk-dev] [PATCH v2 3/6] net/vmxnet3: Generate link-state change notifications Charles (Chas) Williams
2017-06-27 13:52 ` Ferruh Yigit
2017-06-15 12:16 ` [dpdk-dev] [PATCH v2 4/6] net/vmxnet3: Make vmxnet3_process_events less noisy Charles (Chas) Williams
2017-06-28 11:30 ` [dpdk-dev] [PATCH V2 0/6] some local vmxnet3 patches Ferruh Yigit
2017-06-28 12:52 ` Ferruh Yigit
2017-06-28 13:09 ` Charles (Chas) Williams
2017-06-28 17:15 ` Charles (Chas) Williams
2017-06-28 17:54 ` Ferruh Yigit
2017-06-15 12:17 ` [dpdk-dev] [PATCH v2 5/6] net/vmxnet3: receive queue memory leak Charles (Chas) Williams
2017-06-23 23:00 ` Shrikrishna Khare
2017-06-15 12:17 ` [dpdk-dev] [PATCH v2 6/6] net/vmxnet3: preserve configured MAC address Charles (Chas) Williams
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