Revision 7ba1b689038726d34e3244c1ac9e2e18c2ea4787 authored by Ralf Baechle on 09 February 2017, 13:12:11 UTC, committed by David S. Miller on 10 February 2017, 18:41:13 UTC
If a USB-to-serial adapter is unplugged, the driver re-initializes, with dev->hard_header_len and dev->addr_len set to zero, instead of the correct values. If then a packet is sent through the half-dead interface, the kernel will panic due to running out of headroom in the skb when pushing for the AX.25 headers resulting in this panic: [<c0595468>] (skb_panic) from [<c0401f70>] (skb_push+0x4c/0x50) [<c0401f70>] (skb_push) from [<bf0bdad4>] (ax25_hard_header+0x34/0xf4 [ax25]) [<bf0bdad4>] (ax25_hard_header [ax25]) from [<bf0d05d4>] (ax_header+0x38/0x40 [mkiss]) [<bf0d05d4>] (ax_header [mkiss]) from [<c041b584>] (neigh_compat_output+0x8c/0xd8) [<c041b584>] (neigh_compat_output) from [<c043e7a8>] (ip_finish_output+0x2a0/0x914) [<c043e7a8>] (ip_finish_output) from [<c043f948>] (ip_output+0xd8/0xf0) [<c043f948>] (ip_output) from [<c043f04c>] (ip_local_out_sk+0x44/0x48) This patch makes mkiss behave like the 6pack driver. 6pack does not panic. In 6pack.c sp_setup() (same function name here) the values for dev->hard_header_len and dev->addr_len are set to the same values as in my mkiss patch. [ralf@linux-mips.org: Massages original submission to conform to the usual standards for patch submissions.] Signed-off-by: Thomas Osterried <thomas@osterried.de> Signed-off-by: Ralf Baechle <ralf@linux-mips.org> Signed-off-by: David S. Miller <davem@davemloft.net>
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boost.txt
Processor boosting control
- information for users -
Quick guide for the impatient:
--------------------
/sys/devices/system/cpu/cpufreq/boost
controls the boost setting for the whole system. You can read and write
that file with either "0" (boosting disabled) or "1" (boosting allowed).
Reading or writing 1 does not mean that the system is boosting at this
very moment, but only that the CPU _may_ raise the frequency at it's
discretion.
--------------------
Introduction
-------------
Some CPUs support a functionality to raise the operating frequency of
some cores in a multi-core package if certain conditions apply, mostly
if the whole chip is not fully utilized and below it's intended thermal
budget. The decision about boost disable/enable is made either at hardware
(e.g. x86) or software (e.g ARM).
On Intel CPUs this is called "Turbo Boost", AMD calls it "Turbo-Core",
in technical documentation "Core performance boost". In Linux we use
the term "boost" for convenience.
Rationale for disable switch
----------------------------
Though the idea is to just give better performance without any user
intervention, sometimes the need arises to disable this functionality.
Most systems offer a switch in the (BIOS) firmware to disable the
functionality at all, but a more fine-grained and dynamic control would
be desirable:
1. While running benchmarks, reproducible results are important. Since
the boosting functionality depends on the load of the whole package,
single thread performance can vary. By explicitly disabling the boost
functionality at least for the benchmark's run-time the system will run
at a fixed frequency and results are reproducible again.
2. To examine the impact of the boosting functionality it is helpful
to do tests with and without boosting.
3. Boosting means overclocking the processor, though under controlled
conditions. By raising the frequency and the voltage the processor
will consume more power than without the boosting, which may be
undesirable for instance for mobile users. Disabling boosting may
save power here, though this depends on the workload.
User controlled switch
----------------------
To allow the user to toggle the boosting functionality, the cpufreq core
driver exports a sysfs knob to enable or disable it. There is a file:
/sys/devices/system/cpu/cpufreq/boost
which can either read "0" (boosting disabled) or "1" (boosting enabled).
The file is exported only when cpufreq driver supports boosting.
Explicitly changing the permissions and writing to that file anyway will
return EINVAL.
On supported CPUs one can write either a "0" or a "1" into this file.
This will either disable the boost functionality on all cores in the
whole system (0) or will allow the software or hardware to boost at will
(1).
Writing a "1" does not explicitly boost the system, but just allows the
CPU to boost at their discretion. Some implementations take external
factors like the chip's temperature into account, so boosting once does
not necessarily mean that it will occur every time even using the exact
same software setup.
AMD legacy cpb switch
---------------------
The AMD powernow-k8 driver used to support a very similar switch to
disable or enable the "Core Performance Boost" feature of some AMD CPUs.
This switch was instantiated in each CPU's cpufreq directory
(/sys/devices/system/cpu[0-9]*/cpufreq) and was called "cpb".
Though the per CPU existence hints at a more fine grained control, the
actual implementation only supported a system-global switch semantics,
which was simply reflected into each CPU's file. Writing a 0 or 1 into it
would pull the other CPUs to the same state.
For compatibility reasons this file and its behavior is still supported
on AMD CPUs, though it is now protected by a config switch
(X86_ACPI_CPUFREQ_CPB). On Intel CPUs this file will never be created,
even with the config option set.
This functionality is considered legacy and will be removed in some future
kernel version.
More fine grained boosting control
----------------------------------
Technically it is possible to switch the boosting functionality at least
on a per package basis, for some CPUs even per core. Currently the driver
does not support it, but this may be implemented in the future.
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