From: "Bjørn Mork" <bjorn@mork•no>
To: Jim Baxter <jim_baxter@mentor•com>
Cc: <linux-usb@vger•kernel.org>, <netdev@vger•kernel.org>,
<linux-kernel@vger•kernel.org>, Oliver Neukum <oliver@neukum•org>
Subject: Re: [RFC V1 1/1] net: cdc_ncm: Reduce memory use when kernel memory low
Date: Tue, 16 May 2017 20:24:10 +0200 [thread overview]
Message-ID: <87shk4fynp.fsf@miraculix.mork.no> (raw)
In-Reply-To: <1494956480-6127-2-git-send-email-jim_baxter@mentor.com> (Jim Baxter's message of "Tue, 16 May 2017 18:41:20 +0100")
Jim Baxter <jim_baxter@mentor•com> writes:
> The CDC-NCM driver can require large amounts of memory to create
> skb's and this can be a problem when the memory becomes fragmented.
>
> This especially affects embedded systems that have constrained
> resources but wish to maximise the throughput of CDC-NCM with 16KiB
> NTB's.
>
> The issue is after running for a while the kernel memory can become
> fragmented and it needs compacting.
> If the NTB allocation is needed before the memory has been compacted
> the atomic allocation can fail which can cause increased latency,
> large re-transmissions or disconnections depending upon the data
> being transmitted at the time.
> This situation occurs for less than a second until the kernel has
> compacted the memory but the failed devices can take a lot longer to
> recover from the failed TX packets.
>
> To ease this temporary situation I modified the CDC-NCM TX path to
> temporarily switch into a reduced memory mode which allocates an NTB
> that will fit into a USB_CDC_NCM_NTB_MIN_OUT_SIZE (default 2048 Bytes)
> sized memory block and only transmit NTB's with a single network frame
> until the memory situation is resolved.
> Once the memory is compacted the CDC-NCM data can resume transmitting
> at the normal tx_max rate once again.
I must say that I don't like the additional complexity added here. If
there are memory issues and you can reduce the buffer size to
USB_CDC_NCM_NTB_MIN_OUT_SIZE, then why don't you just set a lower tx_max
buffer size in the first place?
echo 2048 > /sys/class/net/wwan0/cdc_ncm/tx_max
Bjørn
next prev parent reply other threads:[~2017-05-16 18:24 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-05-16 17:41 [RFC V1 0/1] Reduce cdc_ncm memory use when kernel memory low Jim Baxter
[not found] ` <1494956480-6127-1-git-send-email-jim_baxter-nmGgyN9QBj3QT0dZR+AlfA@public.gmane.org>
2017-05-16 17:41 ` [RFC V1 1/1] net: cdc_ncm: Reduce " Jim Baxter
2017-05-16 18:24 ` Bjørn Mork [this message]
[not found] ` <87shk4fynp.fsf-3F4PFWf5pNjpjLOzFPqGjWGXanvQGlWp@public.gmane.org>
2017-05-17 7:44 ` Oliver Neukum
2017-05-17 10:56 ` Baxter, Jim
2017-05-17 18:18 ` David Miller
2017-05-18 10:01 ` Oliver Neukum
2017-05-22 15:45 ` Baxter, Jim
2017-05-22 15:54 ` David Miller
2017-05-23 8:42 ` Oliver Neukum
2017-05-23 15:26 ` David Miller
2017-05-23 19:06 ` Baxter, Jim
[not found] ` <1497263047.15677.13.camel@suse.com>
2017-06-12 12:32 ` Baxter, Jim
2017-05-19 11:10 ` David Laight
2017-05-19 13:55 ` Bjørn Mork
2017-05-19 14:46 ` David Laight
[not found] ` <063D6719AE5E284EB5DD2968C1650D6DCFFFAC2B-VkEWCZq2GCInGFn1LkZF6NBPR1lH4CV8@public.gmane.org>
2017-05-22 13:27 ` Oliver Neukum
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