From 0f8de4902fe3f3512ee5043c5277d002a488a804 Mon Sep 17 00:00:00 2001 From: Michael Trapp Date: Thu, 10 Mar 2022 13:18:52 +0100 Subject: [PATCH] libuuid: extend cache in uuid_generate_time_generic() Improve throughput and reduce clock sequence increments for high load situation with time based version 1 uuids. In a high load scenario, where an application continiously reads time based version 1 uuids from uuidd, we have noticed the following behaviour. The application reads more uuids as there are available in the corresponding timeframe and each bulk request results in an increment of the clock sequence because of the 'step back' in time. Due to the 14bit size of the clock sequence this also results in overflows of the clock sequence. As uuidd calls uuid_generate_time_safe() uuid_generate_time_generic() the default value for the bulk request in the '#ifdef HAVE_TLS' section of uuid_generate_time_generic() is set to 1000. Extending the 'cache' of uuid_generate_time_generic() by increasing the default of num to 1000000 doesn't solve the issue, but reduces the clock sequence increments by factor 1000 and it also improves the uuid throughput in our setup by factor 3-4. It might be possible to implement a cache for UUIDD_OP_BULK_TIME_UUID UUIDD_OP_TIME_UUID in the uuidd request handling, but it would not be as simple as this fix in uuid_generate_time_generic(). Signed-off-by: Karel Zak --- libuuid/src/gen_uuid.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/libuuid/src/gen_uuid.c b/libuuid/src/gen_uuid.c index d353fa1a0..76d5371ea 100644 --- a/libuuid/src/gen_uuid.c +++ b/libuuid/src/gen_uuid.c @@ -453,7 +453,7 @@ static int uuid_generate_time_generic(uuid_t out) { num = 0; } if (num <= 0) { - num = 1000; + num = 1000000; if (get_uuid_via_daemon(UUIDD_OP_BULK_TIME_UUID, out, &num) == 0) { last_time = time(NULL); -- 2.35.1