Re: [RFC 2/6] PM: Hibernate: Add option to disable disk offset randomization

[Andrew Lunn <andrew@lunn.ch>]

On Wed, May 18, 2022 at 01:18:37PM +0530, Vivek Kumar wrote:
> Add a kernel parameter to disable the disk offset randomization
> for SSD devices in which such feature is available at the
> firmware level. This is helpful in improving hibernation
> resume time.
> 
> Signed-off-by: Vivek Kumar <quic_vivekuma@quicinc.com>
> Signed-off-by: Prasanna Kumar <quic_kprasan@quicinc.com>
> ---
>  Documentation/admin-guide/kernel-parameters.txt | 11 +++++++++++
>  kernel/power/swap.c                             |  9 +++++++++
>  2 files changed, 20 insertions(+)
> 
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 666ade9..06b4f10 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -5192,6 +5192,17 @@
>  			Useful for devices that are detected asynchronously
>  			(e.g. USB and MMC devices).
>  
> +	noswap_randomize
> +			Kernel uses random disk offsets to help with wear-levelling
> +			of SSD devices, while saving the hibernation snapshot image to
> +			disk. Use this parameter to disable this feature for SSD
> +			devices in scenarios when, such randomization is addressed at
> +			the firmware level and hibenration image is not re-generated
> +			frequently.
> +			(Useful for improving hibernation resume time as snapshot pages
> +			are available in disk serially and can be read in bigger chunks
> +			without seeking)

Seeking is a NOP for SSD, so it seems odd you mentioned that. Is the
real problem here that the bootloader driver is very simple, it does
not queue multiple reads to the hardware, but does it one block at a
time?

Do you have performance numbers for both the bootloader and Linux?
Does Linux performance reading the snapshot increase as much as for
the bootloader?

	Andrew