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[PATCH RFC 13/13] migration: Send requested page directly in rp-return t
From: |
Peter Xu |
Subject: |
[PATCH RFC 13/13] migration: Send requested page directly in rp-return thread |
Date: |
Mon, 29 Aug 2022 12:56:59 -0400 |
With all the facilities ready, send the requested page directly in the
rp-return thread rather than queuing it in the request queue, if and only
if postcopy preempt is enabled. It can achieve so because it uses separate
channel for sending urgent pages. The only shared data is bitmap and it's
protected by the bitmap_mutex.
Signed-off-by: Peter Xu <peterx@redhat.com>
---
migration/ram.c | 108 ++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 108 insertions(+)
diff --git a/migration/ram.c b/migration/ram.c
index ef89812c69..e731a70255 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -539,6 +539,8 @@ static QemuThread *decompress_threads;
static QemuMutex decomp_done_lock;
static QemuCond decomp_done_cond;
+static int ram_save_host_page_urgent(PageSearchStatus *pss);
+
static bool do_compress_ram_page(QEMUFile *f, z_stream *stream, RAMBlock
*block,
ram_addr_t offset, uint8_t *source_buf);
@@ -553,6 +555,16 @@ static void pss_init(PageSearchStatus *pss, RAMBlock *rb,
ram_addr_t page)
pss->complete_round = false;
}
+/*
+ * Check whether two PSSs are actively sending the same page. Return true
+ * if it is, false otherwise.
+ */
+static bool pss_overlap(PageSearchStatus *pss1, PageSearchStatus *pss2)
+{
+ return pss1->host_page_sending && pss2->host_page_sending &&
+ (pss1->host_page_start == pss2->host_page_start);
+}
+
static void *do_data_compress(void *opaque)
{
CompressParam *param = opaque;
@@ -2250,6 +2262,53 @@ int ram_save_queue_pages(const char *rbname, ram_addr_t
start, ram_addr_t len)
return -1;
}
+ /*
+ * When with postcopy preempt, we send back the page directly in the
+ * rp-return thread.
+ */
+ if (postcopy_preempt_active()) {
+ ram_addr_t page_start = start >> TARGET_PAGE_BITS;
+ size_t page_size = qemu_ram_pagesize(ramblock);
+ PageSearchStatus *pss = &ram_state->pss[RAM_CHANNEL_POSTCOPY];
+ int ret = 0;
+
+ qemu_mutex_lock(&rs->bitmap_mutex);
+
+ pss_init(pss, ramblock, page_start);
+ /* Always use the preempt channel, and make sure it's there */
+ pss->pss_channel = migrate_get_current()->postcopy_qemufile_src;
+ pss->postcopy_requested = true;
+ assert(pss->pss_channel);
+
+ /*
+ * It must be either one or multiple of host page size. Just
+ * assert; if something wrong we're mostly split brain anyway.
+ */
+ assert(len % page_size == 0);
+ while (len) {
+ if (ram_save_host_page_urgent(pss)) {
+ error_report("%s: ram_save_host_page_urgent() failed: "
+ "ramblock=%s, start_addr=0x"RAM_ADDR_FMT,
+ __func__, ramblock->idstr, start);
+ ret = -1;
+ break;
+ }
+ /*
+ * NOTE: after ram_save_host_page_urgent() succeeded, pss->page
+ * will automatically be moved and point to the next host page
+ * we're going to send, so no need to update here.
+ *
+ * Normally QEMU never sends >1 host page in requests, so
+ * logically we don't even need that as the loop should only
+ * run once, but just to be consistent.
+ */
+ len -= page_size;
+ };
+ qemu_mutex_unlock(&rs->bitmap_mutex);
+
+ return ret;
+ }
+
struct RAMSrcPageRequest *new_entry =
g_new0(struct RAMSrcPageRequest, 1);
new_entry->rb = ramblock;
@@ -2528,6 +2587,55 @@ static void pss_host_page_finish(PageSearchStatus *pss)
pss->host_page_end = 0;
}
+/*
+ * Send an urgent host page specified by `pss'. Need to be called with
+ * bitmap_mutex held.
+ *
+ * Returns 0 if save host page succeeded, false otherwise.
+ */
+static int ram_save_host_page_urgent(PageSearchStatus *pss)
+{
+ bool page_dirty, sent = false;
+ RAMState *rs = ram_state;
+ int ret = 0;
+
+ trace_postcopy_preempt_send_host_page(pss->block->idstr, pss->page);
+ pss_host_page_prepare(pss);
+
+ /*
+ * If precopy is sending the same page, let it be done in precopy, or
+ * we could send the same page in two channels and none of them will
+ * receive the whole page.
+ */
+ if (pss_overlap(pss, &ram_state->pss[RAM_CHANNEL_PRECOPY])) {
+ trace_postcopy_preempt_hit(pss->block->idstr,
+ pss->page << TARGET_PAGE_BITS);
+ return 0;
+ }
+
+ do {
+ page_dirty = migration_bitmap_clear_dirty(rs, pss->block, pss->page);
+
+ if (page_dirty) {
+ /* Be strict to return code; it must be 1, or what else? */
+ if (ram_save_target_page(rs, pss) != 1) {
+ error_report_once("%s: ram_save_target_page failed", __func__);
+ ret = -1;
+ goto out;
+ }
+ sent = true;
+ }
+ pss_find_next_dirty(pss);
+ } while (pss_within_range(pss));
+out:
+ pss_host_page_finish(pss);
+ /* For urgent requests, flush immediately if sent */
+ if (sent) {
+ qemu_fflush(pss->pss_channel);
+ }
+ return ret;
+}
+
/**
* ram_save_host_page: save a whole host page
*
--
2.32.0
- [PATCH RFC 00/13] migration: Postcopy Preempt-Full, Peter Xu, 2022/08/29
- [PATCH RFC 02/13] migration: Add postcopy_preempt_active(), Peter Xu, 2022/08/29
- [PATCH RFC 01/13] migration: Use non-atomic ops for clear log bitmap, Peter Xu, 2022/08/29
- [PATCH RFC 06/13] migration: Trivial cleanup save_page_header() on same block check, Peter Xu, 2022/08/29
- [PATCH RFC 07/13] migration: Remove RAMState.f references in compression code, Peter Xu, 2022/08/29
- [PATCH RFC 04/13] migration: Cleanup xbzrle zero page cache update logic, Peter Xu, 2022/08/29
- [PATCH RFC 11/13] migration: Make PageSearchStatus part of RAMState, Peter Xu, 2022/08/29
- [PATCH RFC 03/13] migration: Yield bitmap_mutex properly when sending/sleeping, Peter Xu, 2022/08/29
- [PATCH RFC 08/13] migration: Teach PSS about host page, Peter Xu, 2022/08/29
- [PATCH RFC 10/13] migration: Add pss_init(), Peter Xu, 2022/08/29
- [PATCH RFC 13/13] migration: Send requested page directly in rp-return thread,
Peter Xu <=
- [PATCH RFC 05/13] migration: Disallow postcopy preempt to be used with compress, Peter Xu, 2022/08/29
- [PATCH RFC 12/13] migration: Move last_sent_block into PageSearchStatus, Peter Xu, 2022/08/29
- [PATCH RFC 09/13] migration: Introduce pss_channel, Peter Xu, 2022/08/29
- Re: [PATCH RFC 00/13] migration: Postcopy Preempt-Full, Peter Xu, 2022/08/29