Hi!
On 2019-11-12T13:29:16+0000, Andrew Stubbs <a...@codesourcery.com> wrote:
> This patch contributes the GCN libgomp plugin, with the various
> configure and make bits to go with it.
An issue with libgomp GCN plugin 'GCN_SUPPRESS_HOST_FALLBACK' (which is
different from the libgomp-level host-fallback execution):
> --- /dev/null
> +++ b/libgomp/plugin/plugin-gcn.c
> +/* Flag to decide if the runtime should suppress a possible fallback to host
> + execution. */
> +
> +static bool suppress_host_fallback;
> +static void
> +init_environment_variables (void)
> +{
> + [...]
> + if (secure_getenv ("GCN_SUPPRESS_HOST_FALLBACK"))
> + suppress_host_fallback = true;
> + else
> + suppress_host_fallback = false;
> +/* Return true if the HSA runtime can run function FN_PTR. */
> +
> +bool
> +GOMP_OFFLOAD_can_run (void *fn_ptr)
> +{
> + struct kernel_info *kernel = (struct kernel_info *) fn_ptr;
> +
> + init_kernel (kernel);
> + if (kernel->initialization_failed)
> + goto failure;
> +
> + return true;
> +
> +failure:
> + if (suppress_host_fallback)
> + GOMP_PLUGIN_fatal ("GCN host fallback has been suppressed");
> + GCN_WARNING ("GCN target cannot be launched, doing a host fallback\n");
> + return false;
> +}
This originates in the libgomp HSA plugin, where the idea was -- in my
understanding -- that you wouldn't have device code available for all
'fn_ptr's, and in that case transparently (shared-memory system!) do
host-fallback execution. Or, with 'GCN_SUPPRESS_HOST_FALLBACK' set,
you'd get those diagnosed.
This has then been copied into the libgomp GCN plugin (see above).
However, is it really still applicable there; don't we assume that we're
generating device code for all relevant functions? (I suppose everyone
really is testing with 'GCN_SUPPRESS_HOST_FALLBACK' set?) Should we thus
actually remove 'suppress_host_fallback' (that is, make it
always-'true'), including removal of the 'can_run' hook? (I suppose that
even in a future shared-memory "GCN" configuration, we're not expecting
to use this again; expecting always-'true' for 'can_run'?)
Now my actual issue: the libgomp GCN plugin then invented an additional
use of 'GCN_SUPPRESS_HOST_FALLBACK':
> +/* Initialize hsa_context if it has not already been done.
> + Return TRUE on success. */
> +
> +static bool
> +init_hsa_context (void)
> +{
> + hsa_status_t status;
> + int agent_index = 0;
> +
> + if (hsa_context.initialized)
> + return true;
> + init_environment_variables ();
> + if (!init_hsa_runtime_functions ())
> + {
> + GCN_WARNING ("Run-time could not be dynamically opened\n");
> + if (suppress_host_fallback)
> + GOMP_PLUGIN_fatal ("GCN host fallback has been suppressed");
> + return false;
> + }
That is, if 'GCN_SUPPRESS_HOST_FALLBACK' is (routinely) set (for its
original purpose), and you have the libgomp GCN plugin configured, but
don't have 'libhsa-runtime64.so.1' available, you run into a fatal error.
The libgomp nvptx plugin in such cases silently disables the
plugin/device (and thus lets libgomp proper do its thing), and I propose
we do the same here. OK to push the attached
"GCN: Even with 'GCN_SUPPRESS_HOST_FALLBACK' set, failure to
'init_hsa_runtime_functions' is not fatal"?
Grüße
Thomas
>From f037d2d8274940f042633a0ecb18a53942c075f5 Mon Sep 17 00:00:00 2001
From: Thomas Schwinge <tschwi...@baylibre.com>
Date: Thu, 7 Mar 2024 10:43:15 +0100
Subject: [PATCH] GCN: Even with 'GCN_SUPPRESS_HOST_FALLBACK' set, failure to
'init_hsa_runtime_functions' is not fatal
'GCN_SUPPRESS_HOST_FALLBACK' controls the libgomp GCN plugin's capability to
transparently use host-fallback execution for certain device functions; it
shouldn't control failure of libgomp GCN plugin initialization (which libgomp
handles fine: triggering use of a different plugin/device, or general
host-fallback execution, or fatal error, as applicable).
libgomp/
* plugin/plugin-gcn.c (init_hsa_context): Even with
'GCN_SUPPRESS_HOST_FALLBACK' set, failure to
'init_hsa_runtime_functions' is not fatal.
---
libgomp/plugin/plugin-gcn.c | 2 --
1 file changed, 2 deletions(-)
diff --git a/libgomp/plugin/plugin-gcn.c b/libgomp/plugin/plugin-gcn.c
index 2771123252a..464164afb03 100644
--- a/libgomp/plugin/plugin-gcn.c
+++ b/libgomp/plugin/plugin-gcn.c
@@ -1524,8 +1524,6 @@ init_hsa_context (void)
if (!init_hsa_runtime_functions ())
{
GCN_WARNING ("Run-time could not be dynamically opened\n");
- if (suppress_host_fallback)
- GOMP_PLUGIN_fatal ("GCN host fallback has been suppressed");
return false;
}
status = hsa_fns.hsa_init_fn ();
--
2.34.1
