From 2b2340e236c0bba8aaca358ea25a5accd8249fbd Mon Sep 17 00:00:00 2001 From: Thomas Schwinge Date: Mon, 27 Feb 2023 16:41:17 +0100 Subject: [PATCH] Allow libgomp 'cbuf' buffering with OpenACC 'async' for 'ephemeral' data This does *allow*, but under no circumstances is this currently going to be used: all potentially applicable data is non-'ephemeral', and thus not considered for 'gomp_coalesce_buf_add' for OpenACC 'async'. (But a use will emerge later.) Follow-up to commit r12-2530-gd88a6951586c7229b25708f4486eaaf4bf4b5bbe "Don't use libgomp 'cbuf' buffering with OpenACC 'async'", addressing this TODO comment: TODO ... but we could allow CBUF usage for EPHEMERAL data? (Open question: is it more performant to use libgomp CBUF buffering or individual device asyncronous copying?) Ephemeral data is small, and therefore individual device asyncronous copying does seem dubious -- in particular given that for all those, we'd individually have to allocate and queue for deallocation a temporary buffer to capture the ephemeral data. Instead, just let the 'cbuf' *be* the temporary buffer. libgomp/ * target.c (gomp_copy_host2dev, gomp_map_vars_internal): Allow libgomp 'cbuf' buffering with OpenACC 'async' for 'ephemeral' data. --- libgomp/target.c | 70 +++++++++++++++++++++++++----------------------- 1 file changed, 36 insertions(+), 34 deletions(-) diff --git a/libgomp/target.c b/libgomp/target.c index 0344f68a936..074caa6a4dc 100644 --- a/libgomp/target.c +++ b/libgomp/target.c @@ -310,10 +310,8 @@ struct gomp_coalesce_buf This must not be used for asynchronous copies, because the host data might not be computed yet (by an earlier asynchronous compute region, for - example). - TODO ... but we could allow CBUF usage for EPHEMERAL data? (Open question: - is it more performant to use libgomp CBUF buffering or individual device - asyncronous copying?) */ + example). The exception is for EPHEMERAL data, that we know is available + already "by construction". */ static inline void gomp_coalesce_buf_add (struct gomp_coalesce_buf *cbuf, size_t start, size_t len) @@ -377,30 +375,6 @@ gomp_copy_host2dev (struct gomp_device_descr *devicep, void *d, const void *h, size_t sz, bool ephemeral, struct gomp_coalesce_buf *cbuf) { - if (__builtin_expect (aq != NULL, 0)) - { - /* See 'gomp_coalesce_buf_add'. */ - assert (!cbuf); - - void *h_buf = (void *) h; - if (ephemeral) - { - /* We're queueing up an asynchronous copy from data that may - disappear before the transfer takes place (i.e. because it is a - stack local in a function that is no longer executing). Make a - copy of the data into a temporary buffer in those cases. */ - h_buf = gomp_malloc (sz); - memcpy (h_buf, h, sz); - } - goacc_device_copy_async (devicep, devicep->openacc.async.host2dev_func, - "dev", d, "host", h_buf, h, sz, aq); - if (ephemeral) - /* Free temporary buffer once the transfer has completed. */ - devicep->openacc.async.queue_callback_func (aq, free, h_buf); - - return; - } - if (cbuf) { uintptr_t doff = (uintptr_t) d - cbuf->tgt->tgt_start; @@ -420,6 +394,12 @@ gomp_copy_host2dev (struct gomp_device_descr *devicep, gomp_mutex_unlock (&devicep->lock); gomp_fatal ("internal libgomp cbuf error"); } + + /* In an asynchronous context, verify that CBUF isn't used + with non-EPHEMERAL data; see 'gomp_coalesce_buf_add'. */ + if (__builtin_expect (aq != NULL, 0)) + assert (ephemeral); + memcpy ((char *) cbuf->buf + (doff - cbuf->chunks[0].start), h, sz); return; @@ -430,7 +410,28 @@ gomp_copy_host2dev (struct gomp_device_descr *devicep, } } - gomp_device_copy (devicep, devicep->host2dev_func, "dev", d, "host", h, sz); + if (__builtin_expect (aq != NULL, 0)) + { + void *h_buf = (void *) h; + if (ephemeral) + { + /* We're queueing up an asynchronous copy from data that may + disappear before the transfer takes place (i.e. because it is a + stack local in a function that is no longer executing). As we've + not been able to use CBUF, make a copy of the data into a + temporary buffer. */ + h_buf = gomp_malloc (sz); + memcpy (h_buf, h, sz); + } + goacc_device_copy_async (devicep, devicep->openacc.async.host2dev_func, + "dev", d, "host", h_buf, h, sz, aq); + if (ephemeral) + /* Free once the transfer has completed. */ + devicep->openacc.async.queue_callback_func (aq, free, h_buf); + } + else + gomp_device_copy (devicep, devicep->host2dev_func, + "dev", d, "host", h, sz); } attribute_hidden void @@ -1751,9 +1752,6 @@ gomp_map_vars_internal (struct gomp_device_descr *devicep, if (cbufp) { - /* See 'gomp_coalesce_buf_add'. */ - assert (!aq); - long c = 0; for (c = 0; c < cbuf.chunk_cnt; ++c) gomp_copy_host2dev (devicep, aq, @@ -1761,8 +1759,12 @@ gomp_map_vars_internal (struct gomp_device_descr *devicep, (char *) cbuf.buf + (cbuf.chunks[c].start - cbuf.chunks[0].start), cbuf.chunks[c].end - cbuf.chunks[c].start, - true, NULL); - free (cbuf.buf); + false, NULL); + if (aq) + /* Free once the transfer has completed. */ + devicep->openacc.async.queue_callback_func (aq, free, cbuf.buf); + else + free (cbuf.buf); cbuf.buf = NULL; cbufp = NULL; } -- 2.25.1