RE: [PATCH 0/13] Parallel struct page initialisation v4

[Elliott, Robert (Server Storage)]

> -----Original Message-----
> From: linux-kernel-owner@xxxxxxxxxxxxxxx [mailto:linux-kernel-
> owner@xxxxxxxxxxxxxxx] On Behalf Of Daniel J Blueman
> Sent: Thursday, April 30, 2015 11:10 AM
> Subject: Re: [PATCH 0/13] Parallel struct page initialisation v4
...
> On a 7TB, 1728-core NumaConnect system with 108 NUMA nodes, we're
> seeing stock 4.0 boot in 7136s. This drops to 2159s, or a 70% reduction
> with this patchset. Non-temporal PMD init [1] drops this to 1045s.
> 
> Nathan, what do you guys see with the non-temporal PMD patch [1]? Do
> add a sfence at the ende label if you manually patch.
> 
...
> [1] https://lkml.org/lkml/2015/4/23/350

From that post:
> +loop_64:
> +	decq  %rcx
> +	movnti	%rax,(%rdi)
> +	movnti	%rax,8(%rdi)
> +	movnti	%rax,16(%rdi)
> +	movnti	%rax,24(%rdi)
> +	movnti	%rax,32(%rdi)
> +	movnti	%rax,40(%rdi)
> +	movnti	%rax,48(%rdi)
> +	movnti	%rax,56(%rdi)
> +	leaq  64(%rdi),%rdi
> +	jnz    loop_64

There are some even more efficient instructions available in x86,
depending on the CPU features:
* movnti		8 byte
* movntdq %xmm		16 byte, SSE
* vmovntdq %ymm	32 byte, AVX
* vmovntdq %zmm	64 byte, AVX-512 (forthcoming)

The last will transfer a full cache line at a time.

For NVDIMMs, the nd pmem driver is also in need of memcpy functions that 
use these non-temporal instructions, both for performance and reliability.
We also need to speed up __clear_page and copy_user_enhanced_string so
userspace accesses through the page cache can keep up.
https://lkml.org/lkml/2015/4/2/453 is one of the threads on that topic.

Some results I've gotten there under different cache attributes
(in terms of 4 KiB IOPS):

16-byte movntdq:
UC write iops=697872 (697.872 K)(0.697872 M)
WB write iops=9745800 (9745.8 K)(9.7458 M)
WC write iops=9801800 (9801.8 K)(9.8018 M)
WT write iops=9812400 (9812.4 K)(9.8124 M)

32-byte vmovntdq:
UC write iops=1274400 (1274.4 K)(1.2744 M)
WB write iops=10259000 (10259 K)(10.259 M)
WC write iops=10286000 (10286 K)(10.286 M)
WT write iops=10294000 (10294 K)(10.294 M)

---
Robert Elliott, HP Server Storage

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