[Crash-utility] [PATCH] diskdump: Optimize the boot time

[Huang Shijie]

Hi Kazu,
On Wed, Mar 30, 2022 at 09:27:18AM +0000, HAGIO KAZUHITO(萩尾 一仁) wrote:
> -----Original Message-----
> > Hi Kazu,
> > On Wed, Mar 30, 2022 at 08:28:19AM +0000, HAGIO KAZUHITO(萩尾 一仁) wrote:
> > > -----Original Message-----
> > > > 1.) The vmcore file maybe very big.
> > > >
> > > >     For example, I have a vmcore file which is over 23G,
> > > >     and the panic kernel had 767.6G memory,
> > > >     its max_sect_len is 4468736.
> > > >
> > > >     Current code costs too much time to do the following loop:
> > > >     ..............................................
> > > >  	for (i = 1; i < max_sect_len + 1; i++) {
> > > >  		dd->valid_pages[i] = dd->valid_pages[i - 1];
> > > > 		for (j = 0; j < BITMAP_SECT_LEN; j++, pfn++)
> > > > 			if (page_is_dumpable(pfn))
> > > > 				dd->valid_pages[i]++;
> > > >     ..............................................
> > > >
> > > >     For my case, it costs about 56 seconds to finish the
> > > >     big loop.
> > > >
> > > >     This patch moves the hweightXX macros to defs.h,
> > > >     and uses hweight64 to optimize the loop.
> > > >
> > > >     For my vmcore, the loop only costs about one second now.
> > > >
> > > > 2.) Tests result:
> > > >   # cat ./commands.txt
> > > >       quit
> > > >
> > > >  Before:
> > > >
> > > >   #echo  3 > /proc/sys/vm/drop_caches;
> > > >   #time ./crash -i ./commands.txt /root/t/vmlinux /root/t/vmcore > /dev/null 2>&1
> > > >    ............................
> > > > 	real    1m54.259s
> > > > 	user    1m12.494s
> > > > 	sys     0m3.857s
> > > >    ............................
> > > >
> > > >  After this patch:
> > > >
> > > >   #echo  3 > /proc/sys/vm/drop_caches;
> > > >   #time ./crash -i ./commands.txt /root/t/vmlinux /root/t/vmcore > /dev/null 2>&1
> > > >    ............................
> > > > 	real    0m55.217s
> > > > 	user    0m15.114s
> > > > 	sys     0m3.560s
> > > >    ............................
> > >
> > > Thank you for the improvement!
> > >
> > > as far as I tested on x86_64 it did not give such a big gain, but looking at
> > > the user time, it will do on arm64.  Lianbo, can you reproduce on arm64?
> > >
> > > with a 192GB x86_64 dumpfile, slightly improved:
> > >
> > > $ time echo quit | ./crash vmlinux dump >/dev/null
> > >
> > > real    0m5.632s
> > Thanks for the testing.
> > 
> > I am curious why it costs only 5.632s for a 192G dumpfile?
> > How much memory of the panic kernel in the dumpfile?
> > 
> > My vmcore has 767.G memory, and the max_sect_len is 4468736.
> 
> I got it with makedumpfile -d 0 and tested it without dropping caches
> to measure the change of the loop cost.  As for memory, which size
> are you saying?  That machine has 192GB memory.
> 
> $ ls -lhs dump
> 193G -rw-------. 1 root root 193G Mar 30 17:07 dump
> $ file dump
> dump: Kdump compressed dump v6, system Linux, ...
> 
> $ ./crash vmlinux dump
> 
>       MEMORY: 191.7 GB
> 
> crash> help -D
> ...
>           block_size: 4096
>         sub_hdr_size: 10
>        bitmap_blocks: 3088
>            max_mapnr: 50593791
> ...
>  total_valid_pages: 50178690
>       max_sect_len: 12352     // added
Ok, it seems your max_sect_len is too small.

> 
> The max_sect_len looks too small comparing yours.. but
>   12352 * 4096 = 50593792

My max_sect_len is 4468736, so
  4468736 / 12352 = 361.78

The (4468736 * 4096) costs 56s on my machine.
Assume our CPU runs at the same speed,
your machine will costs (56/361.78 = 0.1547)s.

So you cannot get big gain. :)	


Thanks
Huang Shijie