From ab38d167c40c995d4b3c3a2ac1347f9f2be9c810 Mon Sep 17 00:00:00 2001 From: "Frank Ch. Eigler" Date: Fri, 4 Jun 2021 08:40:11 -0400 Subject: [PATCH] PR27863: debuginfod optimization for concurrent requests Sometimes, due to configuration error, mishap, or DoS misadventure, a debuginfod server may receive near-concurrent requests for the exact same data from multiple clients. In practically all cases, it is beneficial to the clients, as well as the server, to serialize these requests. This way, debuginfod does not waste CPU in repeatedly & concurrently decompressing large archives or querying upstream servers. Second and later requesters can benefit from the fdcache / client-cache and get their results, probably earlier! This patch adds an "after-you" queueing phase to servicing http-buildid requests, whereby thereads serialize themselves on each query URL being serviced at the moment. Prometheus metrics are added, and the http GET trace line is modified to print the queue+service times separately. Hand-tested on large kernel-debuginfo's, and shows host CPU refusing to multiply in the face of concurrent identical queries. The automated test tries a hundred concurrent curls, at least some of which are slow enough to trigger the "after-you" wait here. Signed-off-by: Frank Ch. Eigler --- debuginfod/ChangeLog | 6 +++ debuginfod/debuginfod.cxx | 75 +++++++++++++++++++++++++++++++++++- tests/ChangeLog | 6 +++ tests/run-debuginfod-find.sh | 14 +++++++ 4 files changed, 100 insertions(+), 1 deletion(-) diff --git a/debuginfod/ChangeLog b/debuginfod/ChangeLog index 21407dc2e..286c910a0 100644 --- a/debuginfod/ChangeLog +++ b/debuginfod/ChangeLog @@ -1,3 +1,9 @@ +2021-06-03 Frank Ch. Eigler + + PR27863 + * debuginfod.cxx (unique_set, unique_set_reserver): New classes. + (handler_cb): Use them to implement "after-you" queueing. + 2021-05-14 Frank Ch. Eigler PR27859 diff --git a/debuginfod/debuginfod.cxx b/debuginfod/debuginfod.cxx index e0948eaba..543044c6f 100644 --- a/debuginfod/debuginfod.cxx +++ b/debuginfod/debuginfod.cxx @@ -705,6 +705,54 @@ static workq scanq; // just a single one // idler: thread_main_groom() +//////////////////////////////////////////////////////////////////////// + +// Unique set is a thread-safe structure that lends 'ownership' of a value +// to a thread. Other threads requesting the same thing are made to wait. +// It's like a semaphore-on-demand. +template +class unique_set +{ +private: + set values; + mutex mtx; + condition_variable cv; +public: + unique_set() {} + ~unique_set() {} + + void acquire(const T& value) + { + unique_lock lock(mtx); + while (values.find(value) != values.end()) + cv.wait(lock); + values.insert(value); + } + + void release(const T& value) + { + unique_lock lock(mtx); + // assert (values.find(value) != values.end()); + values.erase(value); + cv.notify_all(); + } +}; + + +// This is the object that's instantiate to uniquely hold a value in a +// RAII-pattern way. +template +class unique_set_reserver +{ +private: + unique_set& please_hold; + T mine; +public: + unique_set_reserver(unique_set& t, const T& value): + please_hold(t), mine(value) { please_hold.acquire(mine); } + ~unique_set_reserver() { please_hold.release(mine); } +}; + //////////////////////////////////////////////////////////////////////// @@ -1961,6 +2009,7 @@ handler_cb (void * /*cls*/, off_t http_size = -1; struct timespec ts_start, ts_end; clock_gettime (CLOCK_MONOTONIC, &ts_start); + double afteryou = 0.0; try { @@ -1973,7 +2022,25 @@ handler_cb (void * /*cls*/, if (slash1 != string::npos && url1 == "/buildid") { + // PR27863: block this thread awhile if another thread is already busy + // fetching the exact same thing. This is better for Everyone. + // The latecomer says "... after you!" and waits. + add_metric ("thread_busy", "role", "http-buildid-after-you", 1); +#ifdef HAVE_PTHREAD_SETNAME_NP + (void) pthread_setname_np (pthread_self(), "mhd-buildid-after-you"); +#endif + struct timespec tsay_start, tsay_end; + clock_gettime (CLOCK_MONOTONIC, &tsay_start); + static unique_set busy_urls; + unique_set_reserver after_you(busy_urls, url1); + clock_gettime (CLOCK_MONOTONIC, &tsay_end); + afteryou = (tsay_end.tv_sec - tsay_start.tv_sec) + (tsay_end.tv_nsec - tsay_start.tv_nsec)/1.e9; + add_metric ("thread_busy", "role", "http-buildid-after-you", -1); + tmp_inc_metric m ("thread_busy", "role", "http-buildid"); +#ifdef HAVE_PTHREAD_SETNAME_NP + (void) pthread_setname_np (pthread_self(), "mhd-buildid"); +#endif size_t slash2 = url_copy.find('/', slash1+1); if (slash2 == string::npos) throw reportable_exception("/buildid/ webapi error, need buildid"); @@ -2036,10 +2103,12 @@ handler_cb (void * /*cls*/, clock_gettime (CLOCK_MONOTONIC, &ts_end); double deltas = (ts_end.tv_sec - ts_start.tv_sec) + (ts_end.tv_nsec - ts_start.tv_nsec)/1.e9; + // afteryou: delay waiting for other client's identical query to complete + // deltas: total latency, including afteryou waiting obatched(clog) << conninfo(connection) << ' ' << method << ' ' << url << ' ' << http_code << ' ' << http_size - << ' ' << (int)(deltas*1000) << "ms" + << ' ' << (int)(afteryou*1000) << '+' << (int)((deltas-afteryou)*1000) << "ms" << endl; // related prometheus metrics @@ -2053,6 +2122,10 @@ handler_cb (void * /*cls*/, deltas*1000); // prometheus prefers _seconds and floating point inc_metric("http_responses_duration_milliseconds_count","code",http_code_str); + add_metric("http_responses_after_you_milliseconds_sum","code",http_code_str, + afteryou*1000); + inc_metric("http_responses_after_you_milliseconds_count","code",http_code_str); + return rc; } diff --git a/tests/ChangeLog b/tests/ChangeLog index 38e92659f..b9e5ed4a5 100644 --- a/tests/ChangeLog +++ b/tests/ChangeLog @@ -1,3 +1,9 @@ +2021-06-03 Frank Ch. Eigler + + PR27863 + * run-debuginfod-find.sh: Test "after-you" queueing via flooding + with concurent curls. + 2021-05-14 Frank Ch. Eigler PR27859 diff --git a/tests/run-debuginfod-find.sh b/tests/run-debuginfod-find.sh index 9183cccb7..0445bce1e 100755 --- a/tests/run-debuginfod-find.sh +++ b/tests/run-debuginfod-find.sh @@ -580,6 +580,20 @@ testrun ${abs_top_builddir}/debuginfod/debuginfod-find debuginfo $BUILDID # Confirm that some debuginfod client pools are being used curl -s http://127.0.0.1:$PORT2/metrics | grep 'dc_pool_op.*reuse' +# Trigger a flood of requests against the same archive content file. +# Use a file that hasn't been previously extracted in to make it +# likely that even this test debuginfod will experience concurrency +# and impose some "after-you" delays. +(for i in `seq 100`; do + curl -s http://127.0.0.1:$PORT1/buildid/87c08d12c78174f1082b7c888b3238219b0eb265/executable >/dev/null & + done; + wait) +curl -s http://127.0.0.1:$PORT1/metrics | grep 'http_responses_after_you.*' +# If we could guarantee some minimum number of seconds of CPU time, we +# could assert that the after_you metrics show some nonzero amount of +# waiting. A few hundred ms is typical on this developer's workstation. + + ######################################################################## # Corrupt the sqlite database and get debuginfod to trip across its errors curl -s http://127.0.0.1:$PORT1/metrics | grep 'sqlite3.*reset' -- 2.39.5