netdev - Re: [PATCH v3 bpf-next 10/10] selftests/bpf: cgroup local storage-based network counters

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Date:   Fri, 28 Sep 2018 11:37:26 +0100
From:   Roman Gushchin <guro@...com>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
CC:     <netdev@...r.kernel.org>, Song Liu <songliubraving@...com>,
        <linux-kernel@...r.kernel.org>, <kernel-team@...com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Alexei Starovoitov <ast@...nel.org>
Subject: Re: [PATCH v3 bpf-next 10/10] selftests/bpf: cgroup local
 storage-based network counters

On Fri, Sep 28, 2018 at 12:28:16PM +0200, Alexei Starovoitov wrote:
> On Fri, Sep 28, 2018 at 11:08:29AM +0100, Roman Gushchin wrote:
> > > > +	/* Some packets can be still in per-cpu cache, but not more than
> > > > +	 * MAX_PERCPU_PACKETS.
> > > > +	 */
> > > > +	packets = netcnt.packets;
> > > > +	for (cpu = 0; cpu < nproc; cpu++) {
> > > > +		if (percpu_netcnt[cpu].packets > 32) {
> > > 
> > > pls use MAX_PERCPU_PACKETS in the above check.
> > > could you also double check that if that #define is changed to 1k or so
> > > the exact "!= 10000" check below still works as expected?
> > 
> > Do you mean adding a new test with a different MAX_PERCPU_PACKETS?
> 
> good idea! If it's easy to compile the same source twice with different
> MAX_PERCPU_PACKETS that would certainly make the test stronger.
> Not sure how feasible though.
> 
> > 
> > > 
> > > > +			printf("Unexpected percpu value: %llu\n",
> > > > +			       percpu_netcnt[cpu].packets);
> > > > +			goto err;
> > > 
> > > > +		}
> > > > +
> > > > +		packets += percpu_netcnt[cpu].packets;
> > > > +	}
> > > > +
> > > > +	/* No packets should be lost */
> > > > +	if (packets != 10000) {
> > > > +		printf("Unexpected packet count: %lu\n", packets);
> > > > +		goto err;
> > > > +	}
> > > > +
> > > > +	/* Let's check that bytes counter value is reasonable */
> > > > +	if (netcnt.bytes < packets * 500 || netcnt.bytes > packets * 1500) {
> > > 
> > > since packet count is accurate why byte count would vary ?
> > 
> > Tbh I'm not sure if the size of the packet here can vary depending
> > on the environment. Is there a nice way to get the expected size?
> 
> ping packets should be fixed size depending on v4 vs v6.
> If 'ping -6' is used, it will force ipv6.
> 

Are we ok to screw up kselftests on v4-only machines?

Alternatively, I can send 1 packet, get the size and check that all other
are of the same size.