The QEMUFile 'save_hook' callback has a 'size_t size' parameter.
The RDMA impl of this has logic that takes different actions
depending on whether the value is zero or non-zero. It has
commented out logic that would have taken further actions
if the value was negative.
The only place where the 'save_hook' callback is invoked is
the ram_control_save_page() method, which passes 'size'
through from its caller. The only caller of this method is
in turn control_save_page(). This method unconditionally
passes the 'TARGET_PAGE_SIZE' constant for the 'size' parameter.
IOW, the only scenario for 'size' that can execute in the
qemu_rdma_save_page method is 'size > 0'. The remaining code
has been unreachable since RDMA support was first introduced
9 years ago.
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
---
migration/rdma.c | 120 +++++++++--------------------------------------
1 file changed, 21 insertions(+), 99 deletions(-)
diff --git a/migration/rdma.c b/migration/rdma.c
index 672d1958a9..6e7756bee7 100644
--- a/migration/rdma.c
+++ b/migration/rdma.c
@@ -1486,34 +1486,6 @@ static uint64_t qemu_rdma_make_wrid(uint64_t wr_id, uint64_t index,
return result;
}
-/*
- * Set bit for unregistration in the next iteration.
- * We cannot transmit right here, but will unpin later.
- */
-static void qemu_rdma_signal_unregister(RDMAContext *rdma, uint64_t index,
- uint64_t chunk, uint64_t wr_id)
-{
- if (rdma->unregistrations[rdma->unregister_next] != 0) {
- error_report("rdma migration: queue is full");
- } else {
- RDMALocalBlock *block = &(rdma->local_ram_blocks.block[index]);
-
- if (!test_and_set_bit(chunk, block->unregister_bitmap)) {
- trace_qemu_rdma_signal_unregister_append(chunk,
- rdma->unregister_next);
-
- rdma->unregistrations[rdma->unregister_next++] =
- qemu_rdma_make_wrid(wr_id, index, chunk);
-
- if (rdma->unregister_next == RDMA_SIGNALED_SEND_MAX) {
- rdma->unregister_next = 0;
- }
- } else {
- trace_qemu_rdma_signal_unregister_already(chunk);
- }
- }
-}
-
/*
* Consult the connection manager to see a work request
* (of any kind) has completed.
@@ -3278,23 +3250,7 @@ qio_channel_rdma_shutdown(QIOChannel *ioc,
* Offset is an offset to be added to block_offset and used
* to also lookup the corresponding RAMBlock.
*
- * @size > 0 :
- * Initiate an transfer this size.
- *
- * @size == 0 :
- * A 'hint' or 'advice' that means that we wish to speculatively
- * and asynchronously unregister this memory. In this case, there is no
- * guarantee that the unregister will actually happen, for example,
- * if the memory is being actively transmitted. Additionally, the memory
- * may be re-registered at any future time if a write within the same
- * chunk was requested again, even if you attempted to unregister it
- * here.
- *
- * @size < 0 : TODO, not yet supported
- * Unregister the memory NOW. This means that the caller does not
- * expect there to be any future RDMA transfers and we just want to clean
- * things up. This is used in case the upper layer owns the memory and
- * cannot wait for qemu_fclose() to occur.
+ * @size : Number of bytes to transfer
*
* @bytes_sent : User-specificed pointer to indicate how many bytes were
* sent. Usually, this will not be more than a few bytes of
@@ -3323,61 +3279,27 @@ static size_t qemu_rdma_save_page(QEMUFile *f, void *opaque,
qemu_fflush(f);
- if (size > 0) {
- /*
- * Add this page to the current 'chunk'. If the chunk
- * is full, or the page doesn't belong to the current chunk,
- * an actual RDMA write will occur and a new chunk will be formed.
- */
- ret = qemu_rdma_write(f, rdma, block_offset, offset, size);
- if (ret < 0) {
- error_report("rdma migration: write error! %d", ret);
- goto err;
- }
-
- /*
- * We always return 1 bytes because the RDMA
- * protocol is completely asynchronous. We do not yet know
- * whether an identified chunk is zero or not because we're
- * waiting for other pages to potentially be merged with
- * the current chunk. So, we have to call qemu_update_position()
- * later on when the actual write occurs.
- */
- if (bytes_sent) {
- *bytes_sent = 1;
- }
- } else {
- uint64_t index, chunk;
-
- /* TODO: Change QEMUFileOps prototype to be signed: size_t => long
- if (size < 0) {
- ret = qemu_rdma_drain_cq(f, rdma);
- if (ret < 0) {
- fprintf(stderr, "rdma: failed to synchronously drain"
- " completion queue before unregistration.\n");
- goto err;
- }
- }
- */
-
- ret = qemu_rdma_search_ram_block(rdma, block_offset,
- offset, size, &index, &chunk);
-
- if (ret) {
- error_report("ram block search failed");
- goto err;
- }
-
- qemu_rdma_signal_unregister(rdma, index, chunk, 0);
+ /*
+ * Add this page to the current 'chunk'. If the chunk
+ * is full, or the page doesn't belong to the current chunk,
+ * an actual RDMA write will occur and a new chunk will be formed.
+ */
+ ret = qemu_rdma_write(f, rdma, block_offset, offset, size);
+ if (ret < 0) {
+ error_report("rdma migration: write error! %d", ret);
+ goto err;
+ }
- /*
- * TODO: Synchronous, guaranteed unregistration (should not occur during
- * fast-path). Otherwise, unregisters will process on the next call to
- * qemu_rdma_drain_cq()
- if (size < 0) {
- qemu_rdma_unregister_waiting(rdma);
- }
- */
+ /*
+ * We always return 1 bytes because the RDMA
+ * protocol is completely asynchronous. We do not yet know
+ * whether an identified chunk is zero or not because we're
+ * waiting for other pages to potentially be merged with
+ * the current chunk. So, we have to call qemu_update_position()
+ * later on when the actual write occurs.
+ */
+ if (bytes_sent) {
+ *bytes_sent = 1;
}
/*
--
2.36.1
* Daniel P. Berrangé (berrange@redhat.com) wrote:
> The QEMUFile 'save_hook' callback has a 'size_t size' parameter.
>
> The RDMA impl of this has logic that takes different actions
> depending on whether the value is zero or non-zero. It has
> commented out logic that would have taken further actions
> if the value was negative.
>
> The only place where the 'save_hook' callback is invoked is
> the ram_control_save_page() method, which passes 'size'
> through from its caller. The only caller of this method is
> in turn control_save_page(). This method unconditionally
> passes the 'TARGET_PAGE_SIZE' constant for the 'size' parameter.
>
> IOW, the only scenario for 'size' that can execute in the
> qemu_rdma_save_page method is 'size > 0'. The remaining code
> has been unreachable since RDMA support was first introduced
> 9 years ago.
>
> Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
Ah good; less rdma code!
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
> ---
> migration/rdma.c | 120 +++++++++--------------------------------------
> 1 file changed, 21 insertions(+), 99 deletions(-)
>
> diff --git a/migration/rdma.c b/migration/rdma.c
> index 672d1958a9..6e7756bee7 100644
> --- a/migration/rdma.c
> +++ b/migration/rdma.c
> @@ -1486,34 +1486,6 @@ static uint64_t qemu_rdma_make_wrid(uint64_t wr_id, uint64_t index,
> return result;
> }
>
> -/*
> - * Set bit for unregistration in the next iteration.
> - * We cannot transmit right here, but will unpin later.
> - */
> -static void qemu_rdma_signal_unregister(RDMAContext *rdma, uint64_t index,
> - uint64_t chunk, uint64_t wr_id)
> -{
> - if (rdma->unregistrations[rdma->unregister_next] != 0) {
> - error_report("rdma migration: queue is full");
> - } else {
> - RDMALocalBlock *block = &(rdma->local_ram_blocks.block[index]);
> -
> - if (!test_and_set_bit(chunk, block->unregister_bitmap)) {
> - trace_qemu_rdma_signal_unregister_append(chunk,
> - rdma->unregister_next);
> -
> - rdma->unregistrations[rdma->unregister_next++] =
> - qemu_rdma_make_wrid(wr_id, index, chunk);
> -
> - if (rdma->unregister_next == RDMA_SIGNALED_SEND_MAX) {
> - rdma->unregister_next = 0;
> - }
> - } else {
> - trace_qemu_rdma_signal_unregister_already(chunk);
> - }
> - }
> -}
> -
> /*
> * Consult the connection manager to see a work request
> * (of any kind) has completed.
> @@ -3278,23 +3250,7 @@ qio_channel_rdma_shutdown(QIOChannel *ioc,
> * Offset is an offset to be added to block_offset and used
> * to also lookup the corresponding RAMBlock.
> *
> - * @size > 0 :
> - * Initiate an transfer this size.
> - *
> - * @size == 0 :
> - * A 'hint' or 'advice' that means that we wish to speculatively
> - * and asynchronously unregister this memory. In this case, there is no
> - * guarantee that the unregister will actually happen, for example,
> - * if the memory is being actively transmitted. Additionally, the memory
> - * may be re-registered at any future time if a write within the same
> - * chunk was requested again, even if you attempted to unregister it
> - * here.
> - *
> - * @size < 0 : TODO, not yet supported
> - * Unregister the memory NOW. This means that the caller does not
> - * expect there to be any future RDMA transfers and we just want to clean
> - * things up. This is used in case the upper layer owns the memory and
> - * cannot wait for qemu_fclose() to occur.
> + * @size : Number of bytes to transfer
> *
> * @bytes_sent : User-specificed pointer to indicate how many bytes were
> * sent. Usually, this will not be more than a few bytes of
> @@ -3323,61 +3279,27 @@ static size_t qemu_rdma_save_page(QEMUFile *f, void *opaque,
>
> qemu_fflush(f);
>
> - if (size > 0) {
> - /*
> - * Add this page to the current 'chunk'. If the chunk
> - * is full, or the page doesn't belong to the current chunk,
> - * an actual RDMA write will occur and a new chunk will be formed.
> - */
> - ret = qemu_rdma_write(f, rdma, block_offset, offset, size);
> - if (ret < 0) {
> - error_report("rdma migration: write error! %d", ret);
> - goto err;
> - }
> -
> - /*
> - * We always return 1 bytes because the RDMA
> - * protocol is completely asynchronous. We do not yet know
> - * whether an identified chunk is zero or not because we're
> - * waiting for other pages to potentially be merged with
> - * the current chunk. So, we have to call qemu_update_position()
> - * later on when the actual write occurs.
> - */
> - if (bytes_sent) {
> - *bytes_sent = 1;
> - }
> - } else {
> - uint64_t index, chunk;
> -
> - /* TODO: Change QEMUFileOps prototype to be signed: size_t => long
> - if (size < 0) {
> - ret = qemu_rdma_drain_cq(f, rdma);
> - if (ret < 0) {
> - fprintf(stderr, "rdma: failed to synchronously drain"
> - " completion queue before unregistration.\n");
> - goto err;
> - }
> - }
> - */
> -
> - ret = qemu_rdma_search_ram_block(rdma, block_offset,
> - offset, size, &index, &chunk);
> -
> - if (ret) {
> - error_report("ram block search failed");
> - goto err;
> - }
> -
> - qemu_rdma_signal_unregister(rdma, index, chunk, 0);
> + /*
> + * Add this page to the current 'chunk'. If the chunk
> + * is full, or the page doesn't belong to the current chunk,
> + * an actual RDMA write will occur and a new chunk will be formed.
> + */
> + ret = qemu_rdma_write(f, rdma, block_offset, offset, size);
> + if (ret < 0) {
> + error_report("rdma migration: write error! %d", ret);
> + goto err;
> + }
>
> - /*
> - * TODO: Synchronous, guaranteed unregistration (should not occur during
> - * fast-path). Otherwise, unregisters will process on the next call to
> - * qemu_rdma_drain_cq()
> - if (size < 0) {
> - qemu_rdma_unregister_waiting(rdma);
> - }
> - */
> + /*
> + * We always return 1 bytes because the RDMA
> + * protocol is completely asynchronous. We do not yet know
> + * whether an identified chunk is zero or not because we're
> + * waiting for other pages to potentially be merged with
> + * the current chunk. So, we have to call qemu_update_position()
> + * later on when the actual write occurs.
> + */
> + if (bytes_sent) {
> + *bytes_sent = 1;
> }
>
> /*
> --
> 2.36.1
>
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
On Tue, May 24, 2022 at 12:02:18PM +0100, Daniel P. Berrangé wrote: > The QEMUFile 'save_hook' callback has a 'size_t size' parameter. > > The RDMA impl of this has logic that takes different actions > depending on whether the value is zero or non-zero. It has > commented out logic that would have taken further actions > if the value was negative. > > The only place where the 'save_hook' callback is invoked is > the ram_control_save_page() method, which passes 'size' > through from its caller. The only caller of this method is > in turn control_save_page(). This method unconditionally > passes the 'TARGET_PAGE_SIZE' constant for the 'size' parameter. > > IOW, the only scenario for 'size' that can execute in the > qemu_rdma_save_page method is 'size > 0'. The remaining code > has been unreachable since RDMA support was first introduced > 9 years ago. > > Signed-off-by: Daniel P. Berrangé <berrange@redhat.com> > --- > migration/rdma.c | 120 +++++++++-------------------------------------- > 1 file changed, 21 insertions(+), 99 deletions(-) > Reviewed-by: Eric Blake <eblake@redhat.com> -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3266 Virtualization: qemu.org | libvirt.org
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