|
| From: | Alexey Perevalov |
| Subject: | Re: [Qemu-devel] [PATCH v10 07/10] migration: calculate vCPU blocktime on dst side |
| Date: | Thu, 28 Sep 2017 11:01:01 +0300 |
| User-agent: | Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.3.0 |
On 09/21/2017 02:57 PM, Dr. David Alan Gilbert wrote:
* Alexey Perevalov (address@hidden) wrote:This patch provides blocktime calculation per vCPU, as a summary and as a overlapped value for all vCPUs. This approach was suggested by Peter Xu, as an improvements of previous approch where QEMU kept tree with faulted page address and cpus bitmask in it. Now QEMU is keeping array with faulted page address as value and vCPU as index. It helps to find proper vCPU at UFFD_COPY time. Also it keeps list for blocktime per vCPU (could be traced with page_fault_addr) Blocktime will not calculated if postcopy_blocktime field of MigrationIncomingState wasn't initialized. Signed-off-by: Alexey Perevalov <address@hidden> --- migration/postcopy-ram.c | 138 ++++++++++++++++++++++++++++++++++++++++++++++- migration/trace-events | 5 +- 2 files changed, 140 insertions(+), 3 deletions(-) diff --git a/migration/postcopy-ram.c b/migration/postcopy-ram.c index cc78981..9a5133f 100644 --- a/migration/postcopy-ram.c +++ b/migration/postcopy-ram.c @@ -110,7 +110,6 @@ static struct PostcopyBlocktimeContext *blocktime_context_new(void)ctx->exit_notifier.notify = migration_exit_cb;qemu_add_exit_notifier(&ctx->exit_notifier); - add_migration_state_change_notifier(&ctx->postcopy_notifier); return ctx; }@@ -559,6 +558,136 @@ static int ram_block_enable_notify(const char *block_name, void *host_addr,return 0; }+static int get_mem_fault_cpu_index(uint32_t pid)+{ + CPUState *cpu_iter; + + CPU_FOREACH(cpu_iter) { + if (cpu_iter->thread_id == pid) { + trace_get_mem_fault_cpu_index(cpu_iter->cpu_index, pid); + return cpu_iter->cpu_index; + } + } + trace_get_mem_fault_cpu_index(-1, pid); + return -1; +} + +/* + * This function is being called when pagefault occurs. It + * tracks down vCPU blocking time. + * + * @addr: faulted host virtual address + * @ptid: faulted process thread id + * @rb: ramblock appropriate to addr + */ +static void mark_postcopy_blocktime_begin(uint64_t addr, uint32_t ptid, + RAMBlock *rb) +{ + int cpu, already_received; + MigrationIncomingState *mis = migration_incoming_get_current(); + PostcopyBlocktimeContext *dc = mis->blocktime_ctx; + int64_t now_ms; + + if (!dc || ptid == 0) { + return; + } + cpu = get_mem_fault_cpu_index(ptid); + if (cpu < 0) { + return; + } + + now_ms = qemu_clock_get_ms(QEMU_CLOCK_REALTIME); + if (dc->vcpu_addr[cpu] == 0) { + atomic_inc(&dc->smp_cpus_down); + } + + atomic_xchg__nocheck(&dc->vcpu_addr[cpu], addr); + atomic_xchg__nocheck(&dc->last_begin, now_ms); + atomic_xchg__nocheck(&dc->page_fault_vcpu_time[cpu], now_ms); + + already_received = ramblock_recv_bitmap_test(rb, (void *)addr); + if (already_received) { + atomic_xchg__nocheck(&dc->vcpu_addr[cpu], 0); + atomic_xchg__nocheck(&dc->page_fault_vcpu_time[cpu], 0); + atomic_sub(&dc->smp_cpus_down, 1); + } + trace_mark_postcopy_blocktime_begin(addr, dc, dc->page_fault_vcpu_time[cpu], + cpu, already_received); +} + +/* + * This function just provide calculated blocktime per cpu and trace it. + * Total blocktime is calculated in mark_postcopy_blocktime_end. + * + * + * Assume we have 3 CPU + * + * S1 E1 S1 E1 + * -----***********------------xxx***************------------------------> CPU1 + * + * S2 E2 + * ------------****************xxx---------------------------------------> CPU2 + * + * S3 E3 + * ------------------------****xxx********-------------------------------> CPU3 + * + * We have sequence S1,S2,E1,S3,S1,E2,E3,E1 + * S2,E1 - doesn't match condition due to sequence S1,S2,E1 doesn't include CPU3 + * S3,S1,E2 - sequence includes all CPUs, in this case overlap will be S1,E2 - + * it's a part of total blocktime. + * S1 - here is last_begin + * Legend of the picture is following: + * * - means blocktime per vCPU + * x - means overlapped blocktime (total blocktime) + * + * @addr: host virtual address + */ +static void mark_postcopy_blocktime_end(uint64_t addr) +{ + MigrationIncomingState *mis = migration_incoming_get_current(); + PostcopyBlocktimeContext *dc = mis->blocktime_ctx; + int i, affected_cpu = 0; + int64_t now_ms; + bool vcpu_total_blocktime = false; + + if (!dc) { + return; + } + + now_ms = qemu_clock_get_ms(QEMU_CLOCK_REALTIME); + + /* lookup cpu, to clear it, + * that algorithm looks straighforward, but it's not + * optimal, more optimal algorithm is keeping tree or hash + * where key is address value is a list of */ + for (i = 0; i < smp_cpus; i++) { + uint64_t vcpu_blocktime = 0; + if (atomic_fetch_add(&dc->vcpu_addr[i], 0) != addr) { + continue; + } + atomic_xchg__nocheck(&dc->vcpu_addr[i], 0); + vcpu_blocktime = now_ms - + atomic_fetch_add(&dc->page_fault_vcpu_time[i], 0); + affected_cpu += 1; + /* we need to know is that mark_postcopy_end was due to + * faulted page, another possible case it's prefetched + * page and in that case we shouldn't be here */ + if (!vcpu_total_blocktime && + atomic_fetch_add(&dc->smp_cpus_down, 0) == smp_cpus) { + vcpu_total_blocktime = true; + } + /* continue cycle, due to one page could affect several vCPUs */ + dc->vcpu_blocktime[i] += vcpu_blocktime; + }Unfortunately this still isn't thread safe; consider the code in mark_postcopy_blocktime_begin is: 1 check vcpu_addr 2 write vcpu_addr 3 write last_begin 4 write vcpu_time 5 smp_cpus_down++ 6 already_received: 7 write addr = 0 8 write vcpu_time = 0 9 smp_cpus_down-- and this code is: a check vcpu_addr b write vcpu_addr c read vcpu_time d read smp_cpus_down e dec smp_cpus_down if (a) happens after (2) but before (3), (c) and (d) can also happen before (3), and so you end up reading a bogus vcpu_time. This is tricky to get right; if you changed the source to do: 1 check vcpu_addr 3 write last_begin 4 write vcpu_time 5 smp_cpus_down++ 2 write vcpu_addr 6 already_received: 7 write addr = 0 8 write vcpu_time = 0 9 smp_cpus_down-- I think it's safer; if you read a good vcpu_addr you know that the vcpu_time has already been written. However, can this check (a) happen between the new (2) and (7) ? It's slim but I think possibly; on the receiving side we've just set the bitmap flag to say received - if a fault comes in at about the same time then we could end up with 1,3,4,5,2 ab 6 7 8 9 cde So again we end up reading a bogus vcpu_time and double decrement smp_cpus_down. So I think we have to have: a' read vcpu_addr b' read vcpu_time c' if vcpu_addr == addr && vcpu_time != 0 ... d' clear vcpu_addr e' read/dec smp_cpus_down
I think even in this sequence it's possible to have
lookup condition
if (atomic_fetch_add(&dc->vcpu_addr[i], 0) != addr ||
atomic_fetch_add(&dc->page_fault_vcpu_time[i], 0) == 0) {
continue;
}
in you terms it's (not c)
between
atomic_xchg__nocheck(&dc->vcpu_addr[cpu], addr); - (2)
and
atomic_xchg__nocheck(&dc->vcpu_addr[cpu], 0); - (7)
2c7
Probability is lesser, but it still exists.
Here comes up a second bitmap, but it will increase code complexity.
BTW, remind me why we don't protect body of these functions by mutex?
You should comment to say where the order is important as well; because we'll never remember this - it's hairy! (Better suggestions welcome) Dave+ atomic_sub(&dc->smp_cpus_down, affected_cpu); + if (vcpu_total_blocktime) { + dc->total_blocktime += now_ms - atomic_fetch_add(&dc->last_begin, 0); + } + trace_mark_postcopy_blocktime_end(addr, dc, dc->total_blocktime, + affected_cpu); +} + /* * Handle faults detected by the USERFAULT markings */ @@ -636,8 +765,11 @@ static void *postcopy_ram_fault_thread(void *opaque) rb_offset &= ~(qemu_ram_pagesize(rb) - 1); trace_postcopy_ram_fault_thread_request(msg.arg.pagefault.address, qemu_ram_get_idstr(rb), - rb_offset); + rb_offset, + msg.arg.pagefault.feat.ptid);+ mark_postcopy_blocktime_begin((uintptr_t)(msg.arg.pagefault.address),+ msg.arg.pagefault.feat.ptid, rb); /* * Send the request to the source - we want to request one * of our host page sizes (which is >= TPS) @@ -727,6 +859,8 @@ static int qemu_ufd_copy_ioctl(int userfault_fd, void *host_addr, if (!ret) { ramblock_recv_bitmap_set_range(rb, host_addr, pagesize / qemu_target_page_size()); + mark_postcopy_blocktime_end((uint64_t)(uintptr_t)host_addr); + } return ret; } diff --git a/migration/trace-events b/migration/trace-events index d2910a6..01f30fe 100644 --- a/migration/trace-events +++ b/migration/trace-events @@ -114,6 +114,8 @@ process_incoming_migration_co_end(int ret, int ps) "ret=%d postcopy-state=%d" process_incoming_migration_co_postcopy_end_main(void) "" migration_set_incoming_channel(void *ioc, const char *ioctype) "ioc=%p ioctype=%s" migration_set_outgoing_channel(void *ioc, const char *ioctype, const char *hostname) "ioc=%p ioctype=%s hostname=%s" +mark_postcopy_blocktime_begin(uint64_t addr, void *dd, int64_t time, int cpu, int received) "addr: 0x%" PRIx64 ", dd: %p, time: %" PRId64 ", cpu: %d, already_received: %d" +mark_postcopy_blocktime_end(uint64_t addr, void *dd, int64_t time, int affected_cpu) "addr: 0x%" PRIx64 ", dd: %p, time: %" PRId64 ", affected_cpu: %d"# migration/rdma.cqemu_rdma_accept_incoming_migration(void) "" @@ -190,7 +192,7 @@ postcopy_ram_enable_notify(void) "" postcopy_ram_fault_thread_entry(void) "" postcopy_ram_fault_thread_exit(void) "" postcopy_ram_fault_thread_quit(void) "" -postcopy_ram_fault_thread_request(uint64_t hostaddr, const char *ramblock, size_t offset) "Request for HVA=0x%" PRIx64 " rb=%s offset=0x%zx" +postcopy_ram_fault_thread_request(uint64_t hostaddr, const char *ramblock, size_t offset, uint32_t pid) "Request for HVA=0x%" PRIx64 " rb=%s offset=0x%zx pid=%u" postcopy_ram_incoming_cleanup_closeuf(void) "" postcopy_ram_incoming_cleanup_entry(void) "" postcopy_ram_incoming_cleanup_exit(void) "" @@ -199,6 +201,7 @@ save_xbzrle_page_skipping(void) "" save_xbzrle_page_overflow(void) "" ram_save_iterate_big_wait(uint64_t milliconds, int iterations) "big wait: %" PRIu64 " milliseconds, %d iterations" ram_load_complete(int ret, uint64_t seq_iter) "exit_code %d seq iteration %" PRIu64 +get_mem_fault_cpu_index(int cpu, uint32_t pid) "cpu: %d, pid: %u"# migration/exec.cmigration_exec_outgoing(const char *cmd) "cmd=%s" -- 1.9.1-- Dr. David Alan Gilbert / address@hidden / Manchester, UK
-- Best regards, Alexey Perevalov
| [Prev in Thread] | Current Thread | [Next in Thread] |