netdev - Re: [RFC PATCH] net: Provide linear backoff mechanism for constrained resources at the driver

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAHA+R7Ox+6f2Kd9ZyHLez_7rDrQs1vHEZnsoarhYhd9QRVumJw@mail.gmail.com>
Date:	Wed, 21 May 2014 11:05:28 -0700
From:	Cong Wang <cwang@...pensource.com>
To:	Neil Horman <nhorman@...driver.com>
Cc:	netdev <netdev@...r.kernel.org>, David Miller <davem@...emloft.net>
Subject: Re: [RFC PATCH] net: Provide linear backoff mechanism for constrained
 resources at the driver

On Thu, May 8, 2014 at 12:29 PM, Neil Horman <nhorman@...driver.com> wrote:
> What about something like this?  Its not even compile tested, but let me know
> what you think of the idea.  The reasoning behind it is that transient resources
> like dma address ranges in the iommu or swiotlb have the following attributes
>
> 1) they are quickly allocated and freed
>
> 2) Usually handled by simply trying again at some later point in time
>
> 3) Likely to fail again if tried again immediately.
>
> 4) Not condusive to interlocked signaling mechanisms as the time it takes to
> find and signal a waiting tx queue that resources are now available may take
> longer than needed, and may still result in failure, as competing allocators
> may race in and claim said resources during the signaling period.
>
> As such, what if we try something more simple like a linear backoff? In this
> example we add a TX return code that indicates that the driver is not busy, but
> unable to transmit due to resource constraints.  This signals the qdisc layer to
> skip trying to drain this transmit queue for a short period of time, with
> subsequent simmilar errors causing increased backoff.  Once the condition is
> cleared, the backoff delay is removed and operation returns to normal.

Loos like this is a more general issue which should be solved for every
spinlock:

http://thread.gmane.org/gmane.linux.kernel/1437186
--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html