From: Ido Schimmel <idosch@idosch.org>
To: Justin Iurman <justin.iurman@uliege.be>
Cc: netdev@vger.kernel.org, davem@davemloft.net, kuba@kernel.org,
dsahern@kernel.org, yoshfuji@linux-ipv6.org
Subject: Re: [PATCH net-next v2] ipv6: ioam: Support for Queue depth data field
Date: Sun, 26 Dec 2021 15:15:14 +0200 [thread overview]
Message-ID: <Ychq4ggTdpVG24Zp@shredder> (raw)
In-Reply-To: <462116834.246327590.1640523548154.JavaMail.zimbra@uliege.be>
On Sun, Dec 26, 2021 at 01:59:08PM +0100, Justin Iurman wrote:
> On Dec 26, 2021, at 1:40 PM, Ido Schimmel idosch@idosch.org wrote:
> > On Sun, Dec 26, 2021 at 12:47:51PM +0100, Justin Iurman wrote:
> >> On Dec 24, 2021, at 6:53 PM, Ido Schimmel idosch@idosch.org wrote:
> >> > Why 'qlen' is used and not 'backlog'? From the paragraph you quoted it
> >> > seems that queue depth needs to take into account the size of the
> >> > enqueued packets, not only their number.
> >>
> >> The quoted paragraph contains the following sentence:
> >>
> >> "The queue depth is expressed as the current amount of memory
> >> buffers used by the queue"
> >>
> >> So my understanding is that we need their number, not their size.
> >
> > It also says "a packet could consume one or more memory buffers,
> > depending on its size". If, for example, you define tc-red limit as 1M,
> > then it makes a lot of difference if the 1,000 packets you have in the
> > queue are 9,000 bytes in size or 64 bytes.
>
> Agree. We probably could use 'backlog' instead, regarding this
> statement:
>
> "It should be noted that the semantics of some of the node data fields
> that are defined below, such as the queue depth and buffer occupancy,
> are implementation specific. This approach is intended to allow IOAM
> nodes with various different architectures."
>
> It would indeed make more sense, based on your example. However, the
> limit (32 bits) could be reached faster using 'backlog' rather than
> 'qlen'. But I guess this tradeoff is the price to pay to be as close
> as possible to the spec.
At least in Linux 'backlog' is 32 bits so we are OK :)
We don't have such big buffers in hardware and I'm not sure what
insights an operator will get from a queue depth larger than 4GB...
I just got an OOO auto-reply from my colleague so I'm not sure I will be
able to share his input before next week. Anyway, reporting 'backlog'
makes sense to me, FWIW.
next prev parent reply other threads:[~2021-12-26 13:15 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-12-24 13:50 [PATCH net-next v2] ipv6: ioam: Support for Queue depth data field Justin Iurman
2021-12-24 17:53 ` Ido Schimmel
2021-12-26 11:47 ` Justin Iurman
2021-12-26 12:40 ` Ido Schimmel
2021-12-26 12:59 ` Justin Iurman
2021-12-26 13:15 ` Ido Schimmel [this message]
2021-12-27 14:06 ` Justin Iurman
2021-12-30 14:47 ` Ido Schimmel
2021-12-30 16:50 ` Justin Iurman
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