linux-kernel - Re: [PATCH v3 1/4] powerpc/mobility: wait for memory transfer to complete

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Message-Id: <1657588908.mis26ebam4.astroid@bobo.none>
Date:   Tue, 12 Jul 2022 11:33:07 +1000
From:   Nicholas Piggin <npiggin@...il.com>
To:     benh@...nel.crashing.org, haren@...ux.vnet.ibm.com,
        Laurent Dufour <ldufour@...ux.ibm.com>, linux@...ck-us.net,
        mpe@...erman.id.au, nathanl@...ux.ibm.com, paulus@...ba.org,
        wim@...ux-watchdog.org
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-watchdog@...r.kernel.org
Subject: Re: [PATCH v3 1/4] powerpc/mobility: wait for memory transfer to
 complete

Excerpts from Laurent Dufour's message of June 27, 2022 11:53 pm:
> In pseries_migration_partition(), loop until the memory transfer is
> complete. This way the calling drmgr process will not exit earlier,
> allowing callbacks to be run only once the migration is fully completed.
> 
> If reading the VASI state is done after the hypervisor has completed the
> migration, the HCALL is returning H_PARAMETER. We can safely assume that
> the memory transfer is achieved if this happens.
> 
> This will also allow to manage the NMI watchdog state in the next commits.
> 
> Reviewed-by: Nathan Lynch <nathanl@...ux.ibm.com>
> Signed-off-by: Laurent Dufour <ldufour@...ux.ibm.com>
> ---
>  arch/powerpc/platforms/pseries/mobility.c | 42 +++++++++++++++++++++--
>  1 file changed, 40 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/powerpc/platforms/pseries/mobility.c b/arch/powerpc/platforms/pseries/mobility.c
> index 78f3f74c7056..907a779074d6 100644
> --- a/arch/powerpc/platforms/pseries/mobility.c
> +++ b/arch/powerpc/platforms/pseries/mobility.c
> @@ -427,6 +427,43 @@ static int wait_for_vasi_session_suspending(u64 handle)
>  	return ret;
>  }
>  
> +static void wait_for_vasi_session_completed(u64 handle)
> +{
> +	unsigned long state = 0;
> +	int ret;
> +
> +	pr_info("waiting for memory transfert to complete...\n");

                                            ^ extra t (also below)
> +
> +	/*
> +	 * Wait for transition from H_VASI_RESUMED to H_VASI_COMPLETED.
> +	 */
> +	while (true) {
> +		ret = poll_vasi_state(handle, &state);
> +
> +		/*
> +		 * If the memory transfer is already complete and the migration
> +		 * has been cleaned up by the hypervisor, H_PARAMETER is return,
> +		 * which is translate in EINVAL by poll_vasi_state().
> +		 */
> +		if (ret == -EINVAL || (!ret && state == H_VASI_COMPLETED)) {
> +			pr_info("memory transfert completed.\n");
> +			break;
> +		}
> +
> +		if (ret) {
> +			pr_err("H_VASI_STATE return error (%d)\n", ret);
> +			break;
> +		}
> +
> +		if (state != H_VASI_RESUMED) {
> +			pr_err("unexpected H_VASI_STATE result %lu\n", state);
> +			break;
> +		}
> +
> +		msleep(500);

Is 500 specified anywhere? Another caller uses 1000, and the other one 
uses some backoff interval starting at 1ms...

> +	}
> +}
> +
>  static void prod_single(unsigned int target_cpu)
>  {
>  	long hvrc;
> @@ -673,9 +710,10 @@ static int pseries_migrate_partition(u64 handle)
>  	vas_migration_handler(VAS_SUSPEND);
>  
>  	ret = pseries_suspend(handle);
> -	if (ret == 0)
> +	if (ret == 0) {
>  		post_mobility_fixup();
> -	else
> +		wait_for_vasi_session_completed(handle);

If this wasn't required until later patches, maybe a comment about why 
it's here? Could call it wait_for_migration() or similar too.

Looks okay though from my basic reading of PAPR.

Reviewed-by: Nicholas Piggin <npiggin@...il.com>

> +	} else
>  		pseries_cancel_migration(handle, ret);
>  
>  	vas_migration_handler(VAS_RESUME);
> -- 
> 2.36.1
> 
>