[PATCH] kexec: Allow to skip digest calculation for speed

[Jan H. Schönherr]

On 02/02/2018 02:42 AM, Eric W. Biederman wrote:
> Jan H. Schönherr <jschoenh at amazon.de> writes:
> 
>> Give the administrator the ability to trade kexec safety for kexec speed
>> by disabling the digest calculation/verification for regular kexecs.
>>
>> The behavior of kexec-on-crash is not touched.
> 
> The performance of the digest caculation is acceptable on 386s.  Or it
> was years ago when I tested it on a 386.  What is the problem you are
> having.
> 
> Is there something silly like a cache disable in your configuration?

Last time I measured, this patch reduced the time until the system is responsive
again after a kexec by about 50 ms to 100 ms in my setups. That seems to be about
the right time for enabled caches, judging from a quick sha256sum on the command
line and the kernel sizes I'm working with.

These 50 ms to 100 ms are a noticeable fraction of the total kexec time and they
are easy to avoid -- compared to some other time sinks in the Linux boot process.

Regards
Jan