From: Stephen Hemminger <stephen@networkplumber.org>
To: Ed Czeck <ed.czeck@atomicrules.com>
Cc: dev@dpdk.org
Subject: Re: [dpdk-dev] [PATCH v3 2/7] net/ark: HW API part 1 of 3
Date: Tue, 21 Mar 2017 17:30:29 -0700 [thread overview]
Message-ID: <20170321173029.15af2a76@xeon-e3> (raw)
In-Reply-To: <CALZ3GujU86qSU81Ks+-V9v6XxyKBnL7WB9ukZMZGD66JEqynvw@mail.gmail.com>
On Tue, 21 Mar 2017 20:13:48 -0400
Ed Czeck <ed.czeck@atomicrules.com> wrote:
> Hi Stephen,
>
> Yes I understand the paranoid issue of volatile modifier, which is the
> reason it was coded in this manner.
>
> The struct with volatile are memory mapped IO structures. These structure
> are not instantiated in memory and hence do not incur concurrent (host)
> software access. The a vast majority of the fields as read-only (as viewed
> by the host.) The concurrency model is that hardware is the producer, and
> the host the consumer. There is no handshake other than the host must not
> expect the memory location to remain constant -- that is optimization off.
>
> As for performance, these structures are not in any critical path, so he
> optimization path is correctness not performance.
>
> Do you have a recommendation for changing this code without using the
> volatile modifier? I have requirements from the hardware in the pattern of:
> write a 1 to location x
> read from location y until it become 0
> write a 0 to location x
> How can this work without a volatile modified on x and y?
>
> Best,
> Ed.
Learn to use explicit memory barriers. DPDK has rmb()/wmb() just like kernel.
Once again good explanation of memory barriers in kernel doc.
next prev parent reply other threads:[~2017-03-22 0:30 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-03-21 21:43 [dpdk-dev] [PATCH v3 1/7] net/ark: PMD for Atomic Rules Arkville driver stub Ed Czeck
2017-03-21 21:43 ` [dpdk-dev] [PATCH v3 2/7] net/ark: HW API part 1 of 3 Ed Czeck
2017-03-21 22:15 ` Stephen Hemminger
2017-03-22 0:13 ` Ed Czeck
2017-03-22 0:30 ` Stephen Hemminger [this message]
2017-03-22 14:36 ` Ed Czeck
2017-03-21 21:43 ` [dpdk-dev] [PATCH v3 3/7] net/ark: HW API part 2 " Ed Czeck
2017-03-21 21:43 ` [dpdk-dev] [PATCH v3 4/7] net/ark: HW API part 3 " Ed Czeck
2017-03-21 21:43 ` [dpdk-dev] [PATCH v3 5/7] net/ark: Packet TX support initial version Ed Czeck
2017-03-21 21:43 ` [dpdk-dev] [PATCH v3 6/7] net/ark: Packet RX " Ed Czeck
2017-03-21 21:43 ` [dpdk-dev] [PATCH v3 7/7] net/ark: Arkville PMD component integration Ed Czeck
2017-03-22 18:16 ` [dpdk-dev] [PATCH v3 1/7] net/ark: PMD for Atomic Rules Arkville driver stub Ferruh Yigit
2017-03-23 1:09 ` Ed Czeck
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