Fix typo in 'libgomp.c/target-51.c' (was: [patch] OpenMP: Set default-device-var with OMP_TARGET_OFFLOAD=mandatory)
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Commit Message
Hi!
On 2023-06-13T20:44:39+0200, Tobias Burnus <tobias@codesourcery.com> wrote:
> I intent to commit this tomorrow, unless there are comments.
I'm sorry I'm late. ;-P
> It does as it says (see commit log): It initializes default-device-var
> to the value using the algorithm described in OpenMP 5.2, which
> depends on whether OMP_TARGET_OFFLOAD=mandatory was set.
>
> NOTE: With -foffload=disable there is no binary code but still
> devices get found - such that default-device-var == 0 (= first
> nonhost device). Thus, in that case, libgomp runs the code on that
> device but as no binary data is available, host fallback is used.
> (Even if there would be executable code for another device on
> the system.)
> With mandatory, this unintended host fallback is detected and an
> error is diagnosed. One can argue whether keeping the devices
> makes sense (e.g. because in a dynamic library device code will
> be loaded later) or not (don't list if no code is available).
This reminds me of the (unresolved) <https://gcc.gnu.org/PR81886>
"Means to determine at runtime foffload targets specified at compile time".
> Note that TR11 (future OpenMP 6.0) extends OMP_DEFAULT_DEVICE and
> adds OMP_AVAILABLE_DEVICES which permit a finer-grained control about
> the device, including OMP_DEFAULT_DEVICE=initial (and 'invalid') which
> the current scheme does not permit. (Well, there is
> OMP_TARGET_OFFLOAD=disabled, but that's a too big hammer.)
> PS: DejaGNU testing was done without offloading configured
> and with remote testing on a system having an offload device,
> which which does not support setting environment variables.
> Manual testing was done with offloading enabled and depending
> on the testcase, running on a system with and/or without offloading
> hardware.
> --- a/libgomp/target.c
> +++ b/libgomp/target.c
> @@ -150,7 +150,11 @@ resolve_device (int device_id, bool remapped)
> if (device_id == (remapped ? GOMP_DEVICE_HOST_FALLBACK
> : omp_initial_device))
> return NULL;
> - if (device_id == omp_invalid_device)
> + if (gomp_target_offload_var == GOMP_TARGET_OFFLOAD_MANDATORY
> + && gomp_get_num_devices () == 0)
> + gomp_fatal ("OMP_TARGET_OFFLOAD is set to MANDATORY but only the host "
> + "device is available");
> + else if (device_id == omp_invalid_device)
> gomp_fatal ("omp_invalid_device encountered");
> else if (gomp_target_offload_var == GOMP_TARGET_OFFLOAD_MANDATORY)
> gomp_fatal ("OMP_TARGET_OFFLOAD is set to MANDATORY, "
| "but device not found");
|
| return NULL;
| }
| else if (device_id >= gomp_get_num_devices ())
| {
| if (gomp_target_offload_var == GOMP_TARGET_OFFLOAD_MANDATORY
| && device_id != num_devices_openmp)
| gomp_fatal ("OMP_TARGET_OFFLOAD is set to MANDATORY, "
| "but device not found");
|
| return NULL;
| }
|
| gomp_mutex_lock (&devices[device_id].lock);
| if (devices[device_id].state == GOMP_DEVICE_UNINITIALIZED)
| gomp_init_device (&devices[device_id]);
| else if (devices[device_id].state == GOMP_DEVICE_FINALIZED)
| {
| gomp_mutex_unlock (&devices[device_id].lock);
|
| if (gomp_target_offload_var == GOMP_TARGET_OFFLOAD_MANDATORY)
| gomp_fatal ("OMP_TARGET_OFFLOAD is set to MANDATORY, "
| "but device is finalized");
|
| return NULL;
| }
| gomp_mutex_unlock (&devices[device_id].lock);
|
| return &devices[device_id];
| }
> --- /dev/null
> +++ b/libgomp/testsuite/libgomp.c/target-51.c
> @@ -0,0 +1,24 @@
> +/* Check OMP_TARGET_OFFLOAD on systems with no available non-host devices,
> + which is enforced by using -foffload=disable. */
> +
> +/* { dg-do run } */
> +/* { dg-additional-options "-foffload=disable" } */
> +/* { dg-set-target-env-var OMP_TARGET_OFFLOAD "mandatory" } */
> +
> +/* { dg-shouldfail "OMP_TARGET_OFFLOAD=mandatory and no available device" } */
> +
> +/* See comment in target-50.c/target-50.c for why the output differs. */
> +
> +/* { dg-output ".*libgomp: OMP_TARGET_OFFLOAD is set to MANDATORY but only the host device is available.*" { target { ! offload_device } } } */
> +/* { dg-output ".*libgomp: OMP_TARGET_OFFLOAD is set to MANDATORY but device not found.*" { target offload_device } } */
I intend to push the attached "Fix typo in 'libgomp.c/target-51.c'" after
testing.
Let me know if I should also adjust the new 'target { ! offload_device }'
diagnostic "[...] MANDATORY but only the host device is available" to
include a comma before 'but', for consistency with the other existing
diagnostics (cited above)?
Grüße
Thomas
> +
> +int
> +main ()
> +{
> + int x;
> + #pragma omp target map(tofrom:x)
> + x = 5;
> + if (x != 5)
> + __builtin_abort ();
> + return 0;
> +}
-----------------
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Comments
On 14.06.23 10:09, Thomas Schwinge wrote:
> This reminds me of the (unresolved)https://gcc.gnu.org/PR81886
> "Means to determine at runtime foffload targets specified at compile time".
I think there is the problem that we also support offloading in
libraries. Thus, if you compile the main program without offloading and
then link in a shared offloading-providing library (possibly with
dlopen), it comes (too) late. Thus, we either exclude devices which
could be later used – or we have to live with providing devices
(existing in hardware and with libgomp support) for which no executable
code is available.
As long as the number of devices is not a dynamic property, I guess we
can only handle one or the other.
> I intend to push the attached "Fix typo in 'libgomp.c/target-51.c'"
> after testing.
> Let me know if I should also adjust the new 'target { ! offload_device }'
> diagnostic "[...] MANDATORY but only the host device is available" to
> include a comma before 'but', for consistency with the other existing
> diagnostics (cited above)?
I think it makes sense to be consistent. Thus: Yes, please add the commas.
Thanks,
Tobias
-----------------
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From 2464d87db542b87a1d276637f334e9c6eb35be64 Mon Sep 17 00:00:00 2001
From: Thomas Schwinge <thomas@codesourcery.com>
Date: Wed, 14 Jun 2023 09:25:15 +0200
Subject: [PATCH] Fix typo in 'libgomp.c/target-51.c'
..., and therefore, given 'target offload_device':
PASS: libgomp.c/target-51.c (test for excess errors)
PASS: libgomp.c/target-51.c execution test
[-FAIL:-]{+PASS:+} libgomp.c/target-51.c output pattern test
Fix-up for recent commit 18c8b56c7d67a9e37acf28822587786f0fc0efbc
"OpenMP: Set default-device-var with OMP_TARGET_OFFLOAD=mandatory".
libgomp/
* testsuite/libgomp.c/target-51.c: Fix typo.
---
libgomp/testsuite/libgomp.c/target-51.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
@@ -10,7 +10,7 @@
/* See comment in target-50.c/target-50.c for why the output differs. */
/* { dg-output ".*libgomp: OMP_TARGET_OFFLOAD is set to MANDATORY but only the host device is available.*" { target { ! offload_device } } } */
-/* { dg-output ".*libgomp: OMP_TARGET_OFFLOAD is set to MANDATORY but device not found.*" { target offload_device } } */
+/* { dg-output ".*libgomp: OMP_TARGET_OFFLOAD is set to MANDATORY, but device not found.*" { target offload_device } } */
int
main ()
--
2.39.2