On 8/15/22 16:08, Dionna Amalie Glaze wrote:

quoted

The unpredictable performance of the application early in boot may be
unacceptable and unavoidable. It might take a long time but it could
eventually generate bug reports about "unpredictable performance early
in boot" that will be hard to track down unless accept_memory is observed
using perf at the right time. Even when that does happen, there will need
to be an option to turn it off if the unpredictable performance cannot
be tolerated. Second, any benchmarking done early in boot is likely to
be disrupted making the series a potential bisection magnet that masks a
performance bug elsewhere in the merge window.

I'm doing some boot performance tests now before I run some workload
memory acceptance latency tests.
Note that this testing is on AMD SEV-SNP, so this patch series on top
of the AMD guest patches v12, plus a
patch Brijesh Singh wrote to define __accept_memory for SEV-SNP
https://github.com/AMDESE/linux/commit/ecae2582666d50ce1e633975d703d2f904183ece

Note that there is a bug in Brijesh's version of the patch and it will 
almost exclusively use the MSR protocol. Please try the version of the 
patch that I recently sent up based on the current unaccepted memory tree 
from Kirill.

https://lore.kernel.org/lkml/cover.1660579062.git.thomas.lendacky@amd.com/ (local)

Thanks,
Tom

I was getting pretty consistent boot times, only going up slightly as
the memory size increased, but at 256GB, the VM crashes because it
touches some unaccepted memory without first accepting it. 255GB boots
fine.

The stack track is in mm/page_alloc.c. I've done a little
investigation, but I can't account for why there's a hard cutoff of
correctness at 256GB

[    0.065563] RIP: 0010:memmap_init_range+0x108/0x173
[    0.066309] Code: 77 16 f6 42 10 02 74 10 48 03 42 08 48 c1 e8 0c
48 89 c3 e9 3a ff ff ff 48 89 df 48 c1 e7 06 48 03 3d d9 a2 66 ff 48
8d 47 08 <c7> 47 34 01 00 00 00 48 c7 47 38 00 00 00 00 c7 47 30 ff ff
ff ff
[    0.069108] RSP: 0000:ffffffffad603dc8 EFLAGS: 00010082 ORIG_RAX:
0000000000000404
[    0.070193] RAX: ffffdba740000048 RBX: 0000000000000001 RCX: 0000000000000000
[    0.071170] RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffffdba740000040
[    0.072224] RBP: 0000000000000000 R08: 0000000000001000 R09: 0000000000000000
[    0.073283] R10: 0000000000000001 R11: ffffffffad645c60 R12: 0000000000000000
[    0.074304] R13: 00000000000000a0 R14: 0000000000000000 R15: 0000000000000000
[    0.075285] FS:  0000000000000000(0000) GS:ffffffffadd6c000(0000)
knlGS:0000000000000000
[    0.076365] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[    0.077194] CR2: ffffdba740000074 CR3: 0008001ee3a0c000 CR4: 00000000000606b0
[    0.078209] Call Trace:
[    0.078524]  <TASK>
[    0.078887]  ? free_area_init+0x5c1/0x66c
[    0.079417]  ? zone_sizes_init+0x52/0x6c
[    0.079934]  ? setup_arch+0xa55/0xb6d
[    0.080417]  ? start_kernel+0x64/0x65a
[    0.080897]  ? secondary_startup_64_no_verify+0xd6/0xdb
[    0.081620]  </TASK>

quoted

--
Mel Gorman
SUSE Labs