From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-yw1-f201.google.com (mail-yw1-f201.google.com [209.85.128.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 7D0D61C765 for ; Fri, 2 Jun 2023 16:20:06 +0000 (UTC) Received: by mail-yw1-f201.google.com with SMTP id 00721157ae682-568a85f180dso31571617b3.2 for ; Fri, 02 Jun 2023 09:20:06 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20221208; t=1685722805; x=1688314805; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=PgT1Uj5zI5TzwBHmSWJMIEOClx3Ozd7mBri9eACyvhU=; b=DH+sHpekA4CtcNNFE2ts4GyEJexMMg0gcpP/Pdnx1rkU1sDHqbpzd+MLPkewMSfiAw pf6Mx59ADFAhnPz6Ay8YErOP+qzH9uVKPwoLoLOWjEX1kTiH8UD9WWZFC4k8vAAwQg1m PhTwJ5YpDK6F9LKeOh3Td44IubbolyfnC4Nk6YeLlIvMTpn7wWTkF/3SQQP7r8z6c5Pu PIsqG2FokCpKXOAhs0IGVnYp4jWpuovE2fodhWPnAl8dYIUN9Gc1hR+GKg2cv5/c6+zD lhHIvF4IgvBow0xjvqbGJZMslesbwKDBCbv+bwrDA71OTIjyMTsegJLAYbwFy3iDlyz/ NNvw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1685722805; x=1688314805; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=PgT1Uj5zI5TzwBHmSWJMIEOClx3Ozd7mBri9eACyvhU=; b=d/WCzc9pJnmhesYdVtjPz6+bEjhazIDY6bRUMflvCiZ0R8ogJevJS0bVMFKgOSvSmG bmJ7GfXKvCEF/bqpvicMl/P72hM0LrvgXjiNZgR1YKNvnwjKZ7uwLnXbPSYDVwIpc6uR tY3fQcj7i2ohgV+UtdSlbLJF0IB+wqko2sI0OpxPCMf/W0ZXz7AZWCTHR2tZB95ZLRYn kBx9iSLO8NkHXf6BMHx4V8efhkR4IStlUQGhLF/mGaMOvrXvm4FXHoFfQNosSik3k9to 8VBn1orqBblCXED8PHPx2zWXV6POBj6/hZ8Ls6cJP84Jzedsp6ssO4Hemi2KXc6IHgQO RkzQ== X-Gm-Message-State: AC+VfDwf1Fjf3vlxsx/dPue4Prm22sNaSRGVQ0+wVldJy3/r89BrWGN+ JKO2JpJcZFVIe24408yXH0L0MNfRmjubWw== X-Google-Smtp-Source: ACHHUZ6FuEoBJYVj6pYeKpfGgq/woKRX0q7sUC5NxE1Bbdm0MKKd8BKDYRrzajT7ySnJCtTNqv1sGxdIHbreyg== X-Received: from laogai.c.googlers.com ([fda3:e722:ac3:cc00:2b:7d90:c0a8:2c9]) (user=amoorthy job=sendgmr) by 2002:a5b:804:0:b0:bac:a7d5:f895 with SMTP id x4-20020a5b0804000000b00baca7d5f895mr1209528ybp.10.1685722805363; Fri, 02 Jun 2023 09:20:05 -0700 (PDT) Date: Fri, 2 Jun 2023 16:19:19 +0000 In-Reply-To: <20230602161921.208564-1-amoorthy@google.com> Precedence: bulk X-Mailing-List: kvmarm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20230602161921.208564-1-amoorthy@google.com> X-Mailer: git-send-email 2.41.0.rc0.172.g3f132b7071-goog Message-ID: <20230602161921.208564-15-amoorthy@google.com> Subject: [PATCH v4 14/16] KVM: selftests: Use EPOLL in userfaultfd_util reader threads and signal errors via TEST_ASSERT From: Anish Moorthy To: seanjc@google.com, oliver.upton@linux.dev, kvm@vger.kernel.org, kvmarm@lists.linux.dev Cc: pbonzini@redhat.com, maz@kernel.org, robert.hoo.linux@gmail.com, jthoughton@google.com, amoorthy@google.com, bgardon@google.com, dmatlack@google.com, ricarkol@google.com, axelrasmussen@google.com, peterx@redhat.com, nadav.amit@gmail.com, isaku.yamahata@gmail.com Content-Type: text/plain; charset="UTF-8" With multiple reader threads POLLing a single UFFD, the test suffers from the thundering herd problem: performance degrades as the number of reader threads is increased. Solve this issue [1] by switching the the polling mechanism to EPOLL + EPOLLEXCLUSIVE. Also, change the error-handling convention of uffd_handler_thread_fn. Instead of just printing errors and returning early from the polling loop, check for them via TEST_ASSERT. "return NULL" is reserved for a successful exit from uffd_handler_thread_fn, ie one triggered by a write to the exit pipe. Performance samples generated by the command in [2] are given below. Num Reader Threads, Paging Rate (POLL), Paging Rate (EPOLL) 1 249k 185k 2 201k 235k 4 186k 155k 16 150k 217k 32 89k 198k [1] Single-vCPU performance does suffer somewhat. [2] ./demand_paging_test -u MINOR -s shmem -v 4 -o -r Signed-off-by: Anish Moorthy Acked-by: James Houghton --- .../selftests/kvm/demand_paging_test.c | 1 - .../selftests/kvm/lib/userfaultfd_util.c | 74 +++++++++---------- 2 files changed, 35 insertions(+), 40 deletions(-) diff --git a/tools/testing/selftests/kvm/demand_paging_test.c b/tools/testing/selftests/kvm/demand_paging_test.c index 35935874c690..115194e19ad9 100644 --- a/tools/testing/selftests/kvm/demand_paging_test.c +++ b/tools/testing/selftests/kvm/demand_paging_test.c @@ -13,7 +13,6 @@ #include #include #include -#include #include #include #include diff --git a/tools/testing/selftests/kvm/lib/userfaultfd_util.c b/tools/testing/selftests/kvm/lib/userfaultfd_util.c index 6f220aa4fb08..2a179133645a 100644 --- a/tools/testing/selftests/kvm/lib/userfaultfd_util.c +++ b/tools/testing/selftests/kvm/lib/userfaultfd_util.c @@ -16,6 +16,7 @@ #include #include #include +#include #include #include "kvm_util.h" @@ -32,60 +33,55 @@ static void *uffd_handler_thread_fn(void *arg) int64_t pages = 0; struct timespec start; struct timespec ts_diff; + int epollfd; + struct epoll_event evt; + + epollfd = epoll_create(1); + TEST_ASSERT(epollfd >= 0, "Failed to create epollfd."); + + evt.events = EPOLLIN | EPOLLEXCLUSIVE; + evt.data.u32 = 0; + TEST_ASSERT(epoll_ctl(epollfd, EPOLL_CTL_ADD, uffd, &evt) == 0, + "Failed to add uffd to epollfd"); + + evt.events = EPOLLIN; + evt.data.u32 = 1; + TEST_ASSERT(epoll_ctl(epollfd, EPOLL_CTL_ADD, reader_args->pipe, &evt) == 0, + "Failed to add pipe to epollfd"); clock_gettime(CLOCK_MONOTONIC, &start); while (1) { struct uffd_msg msg; - struct pollfd pollfd[2]; - char tmp_chr; int r; - pollfd[0].fd = uffd; - pollfd[0].events = POLLIN; - pollfd[1].fd = reader_args->pipe; - pollfd[1].events = POLLIN; - - r = poll(pollfd, 2, -1); - switch (r) { - case -1: - pr_info("poll err"); - continue; - case 0: - continue; - case 1: - break; - default: - pr_info("Polling uffd returned %d", r); - return NULL; - } + r = epoll_wait(epollfd, &evt, 1, -1); + TEST_ASSERT(r == 1, + "Unexpected number of events (%d) from epoll, errno = %d", + r, errno); - if (pollfd[0].revents & POLLERR) { - pr_info("uffd revents has POLLERR"); - return NULL; - } + if (evt.data.u32 == 1) { + char tmp_chr; - if (pollfd[1].revents & POLLIN) { - r = read(pollfd[1].fd, &tmp_chr, 1); + TEST_ASSERT(!(evt.events & (EPOLLERR | EPOLLHUP)), + "Reader thread received EPOLLERR or EPOLLHUP on pipe."); + r = read(reader_args->pipe, &tmp_chr, 1); TEST_ASSERT(r == 1, - "Error reading pipefd in UFFD thread\n"); + "Error reading pipefd in uffd reader thread"); break; } - if (!(pollfd[0].revents & POLLIN)) - continue; + TEST_ASSERT(!(evt.events & (EPOLLERR | EPOLLHUP)), + "Reader thread received EPOLLERR or EPOLLHUP on uffd."); r = read(uffd, &msg, sizeof(msg)); if (r == -1) { - if (errno == EAGAIN) - continue; - pr_info("Read of uffd got errno %d\n", errno); - return NULL; + TEST_ASSERT(errno == EAGAIN, + "Error reading from UFFD: errno = %d", errno); + continue; } - if (r != sizeof(msg)) { - pr_info("Read on uffd returned unexpected size: %d bytes", r); - return NULL; - } + TEST_ASSERT(r == sizeof(msg), + "Read on uffd returned unexpected number of bytes (%d)", r); if (!(msg.event & UFFD_EVENT_PAGEFAULT)) continue; @@ -93,8 +89,8 @@ static void *uffd_handler_thread_fn(void *arg) if (reader_args->delay) usleep(reader_args->delay); r = reader_args->handler(reader_args->uffd_mode, uffd, &msg); - if (r < 0) - return NULL; + TEST_ASSERT(r >= 0, + "Reader thread handler fn returned negative value %d", r); pages++; } -- 2.41.0.rc0.172.g3f132b7071-goog