Re: [PATCH v7 1/4] eal: add pointer compression functions

[David Marchand <david.marchand@redhat.com>]

Hello Paul,

Before sending the v8, please fix small issues I found.


On Fri, Mar 1, 2024 at 11:21 AM Paul Szczepanek <paul.szczepanek@arm.com> wrote:
>
> Add a new utility header for compressing pointers. The provided
> functions can store pointers in 32-bit offsets.
>
> The compression takes advantage of the fact that pointers are
> usually located in a limited memory region (like a mempool).
> We can compress them by converting them to offsets from a base
> memory address. Offsets can be stored in fewer bytes (dictated
> by the memory region size and alignment of the pointer).
> For example: an 8 byte aligned pointer which is part of a 32GB
> memory pool can be stored in 4 bytes.
>
> This can be used for example when passing caches full of pointers
> between threads. Memory containing the pointers is copied multiple
> times which is especially costly between cores. This compression
> method will allow us to shrink the memory size copied. Further
> commits add a test to evaluate the effectiveness of this approach.
>
> Suggested-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>
> Signed-off-by: Paul Szczepanek <paul.szczepanek@arm.com>
> Signed-off-by: Kamalakshitha Aligeri <kamalakshitha.aligeri@arm.com>
> Reviewed-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>
> ---
>  lib/eal/include/meson.build        |   1 +
>  lib/eal/include/rte_ptr_compress.h | 266 +++++++++++++++++++++++++++++
>  2 files changed, 267 insertions(+)
>  create mode 100644 lib/eal/include/rte_ptr_compress.h
>
> diff --git a/lib/eal/include/meson.build b/lib/eal/include/meson.build
> index e94b056d46..ce2c733633 100644
> --- a/lib/eal/include/meson.build
> +++ b/lib/eal/include/meson.build
> @@ -36,6 +36,7 @@ headers += files(
>          'rte_pci_dev_features.h',
>          'rte_per_lcore.h',
>          'rte_pflock.h',
> +       'rte_ptr_compress.h',

I suppose it will not be applicable in v8 but:

$ ./devtools/check-meson.py
Error parsing lib/eal/include/meson.build:38, got some tabulation
Error: Incorrect indent at lib/eal/include/meson.build:39


>          'rte_random.h',
>          'rte_reciprocal.h',
>          'rte_seqcount.h',
> diff --git a/lib/eal/include/rte_ptr_compress.h b/lib/eal/include/rte_ptr_compress.h
> new file mode 100644
> index 0000000000..47a72e4213
> --- /dev/null
> +++ b/lib/eal/include/rte_ptr_compress.h
> @@ -0,0 +1,266 @@
> +/* SPDX-License-Identifier: BSD-shift-Clause

Not sure what the "shift" license is.
Typo?

DPDK uses BSD-3-Clause license.

> + * Copyright(c) 2023 Arm Limited

Should be 2024 now.

> + */
> +
> +#ifndef RTE_PTR_COMPRESS_H
> +#define RTE_PTR_COMPRESS_H

For the rest, I'll trust reviewers.


-- 
David Marchand