From: Alan Dewar <alangordondewar@gmail.com>
To: Stephen Hemminger <stephen@networkplumber.org>
Cc: cristian.dumitrescu@intel.com, dev@dpdk.org,
Alan Dewar <alan.dewar@att.com>
Subject: Re: [dpdk-dev] [PATCH] sched: add 64-bit counter retrieval API
Date: Wed, 25 Jul 2018 10:02:23 +0100 [thread overview]
Message-ID: <CAOEQf6h+iRvAgQ_QfitMn8rNdeN+rU3Zto1uS+kkaZxw6eF6ew@mail.gmail.com> (raw)
In-Reply-To: <20180723095252.4a93ea91@xeon-e3>
Hi Stephen,
Sorry about the delay in responding to your comment.
Maybe I'm missing something but I don't consider 64-bit counter
rollover to be a problem.
The DPDK QoS stats are just 32-bits wide and are zeroed when read. So
if we read them frequently enough the 32-bit counters won't wrap.
This new API is just a convenient way to read the 32-bit counters into
variables that are 64-bit wide which allows Vyatta to have a common
API slightly above the DPDK.
I'd hope that at some point in time the DPDK will move to 64-bit
counters, but there may be technical reasons why this can't happen
that I'm not aware of (support for 32-bit CPUs??)
Regards
Alan
On Mon, Jul 23, 2018 at 5:52 PM, Stephen Hemminger
<stephen@networkplumber.org> wrote:
> On Wed, 18 Jul 2018 15:51:39 +0100
> alangordondewar@gmail.com wrote:
>
>> From: Alan Dewar <alan.dewar@att.com>
>>
>> Add new APIs to retrieve counters in 64-bit wide fields.
>>
>> Signed-off-by: Alan Dewar <alan.dewar@att.com>
>
> Do you want to consider 64 bit counter roll over on 32 bit platform?
> The problem is that incrementing an 64 bit value is not atomic on
> 32 bit cpu. The carry operation can race with reading.
>
> The kernel has special case code to do restartable sequence for
> accessing 64 bit counter on 32 bit CPU. These functions become
> nop's on 64bit.
next prev parent reply other threads:[~2018-07-25 9:02 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-07-18 14:51 alangordondewar
2018-07-23 12:33 ` Alan Robertson
2018-07-23 16:52 ` Stephen Hemminger
2018-07-25 9:02 ` Alan Dewar [this message]
2020-06-24 22:51 ` Thomas Monjalon
2020-06-25 8:38 ` Singh, Jasvinder
2020-06-25 9:16 ` Thomas Monjalon
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