{"id":1085,"date":"2019-03-19T15:46:01","date_gmt":"2019-03-19T15:46:01","guid":{"rendered":"http:\/\/www.ankenbrand24.de\/?page_id=1085"},"modified":"2019-03-19T15:51:17","modified_gmt":"2019-03-19T15:51:17","slug":"smt-hyper-threading","status":"publish","type":"page","link":"https:\/\/www.ankenbrand24.de\/index.php\/articles\/check-point-articel\/performance-tuning\/smt-hyper-threading\/","title":{"rendered":"SMT (Hyper Threading)"},"content":{"rendered":"\n
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R80.x Performance Tuning \u2013 SMT (Hyper Threading)<\/span><\/h2>\n\n\n\n
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SMT (Hyper Threading)<\/span><\/th>\n<\/tr>\n<\/thead>\n<\/table>\n

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Hyper Threading Technology is a form of Simultaneous Multithreading Technology (SMT) introduced by Intel. Architecturally, a processor with Hyper-Threading technology consists of two logical processors per core, each of which has its own processor architectural state.Each logical processor can be individually halted, interrupted or directed to execute a specified thread, independently from the other logical processor sharing the same physical core. Unlike a traditional dual-processor configuration that uses two separate physical processors, the logical processors in a hyper-threaded core share the execution resources. These resources include the execution engine, caches, and system bus interface; the sharing of resources allows two logical processors to work with each other more efficiently, and allows a logical processor to borrow resources from a stalled logical core (assuming both logical cores are associated with the same physical core).<\/p>\n

A processor stalls when it is waiting for data it has sent for so it can finish processing the present thread. The degree of benefit seen when using a hyper-threaded or multi core processor depends on the needs of the software, and how well it and the firewall.<\/p>\n

Hyper-Threading works by duplicating certain sections of the processor – those that store the architectural state – but not duplicating the main execution resources. This allows a hyper-threading processor to appear as the usual “physical” processor and an extra “logical” processor to the firewall.<\/p>\n

The number of concurrent threads can be decided by the chip designers. Two concurrent threads per CPU core are common. Because it is really an efficiency technique that inevitably increases conflict on shared resources, measuring or agreeing on its effectiveness can be difficult.<\/p>\n\n\n\n
Preview to Intel Architecture<\/span><\/th>\n<\/tr>\n<\/thead>\n<\/table>\n

The following statement is also often discussed on the Internet:<\/p>\n

SMT can increase message rate for multi process applications by having more logical cores. This increases the latency of a single process due to lower frequency of a single logical core when hyper-threading is enabled. This means interrupt processing of the NICs will be slower, load will be higher and packet rate will decrease. I think that’s why Check Point doesn’t recommend SMT in pure firewall and VPN mode. From my point of view, it only accelerates software balades. Therefore I use it if necessary, if many blades are activated. I’d like to discuss that with Check Point.<\/p>\n

Small example with basic viewing:<\/p>\n

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This presentation is very simplified and should illustrate the issues. If SMT channel 2 uses all core resources with I\/O operations, channel 1 must wait for the core resources. This can reduce the performance with enabled SMT. The same effect can occur with multi-queue and enabled SMT. The problem can be fixed by adjusting the Check Point affinity or disable SMT. What we see here, many Intel architecture issues can affect SMT and therefore the firewall performance.<\/p>\n\n\n\n
Check Point and SMT<\/span><\/th>\n<\/tr>\n<\/thead>\n<\/table>\n

SMT is a feature that is supported on Check Point appliances running Gaia OS. When enabled, SMT doubles the number of logical CPUs on the security gateway, which enhances physical processor utilization. When SMT is disabled, the number of logical CPUs equals the number of physical cores. SMT improves performance up to 30% on software blades such as IPS, Application & URL Filtering and Threat Prevention by increasing the number of CoreXL FW instances based on the number of logical CPUs.<\/p>\n

Turning on SMT can have some side effects in terms of multi-queue and affinity. After turning on SMT the affinity should normally be adjusted.<\/p>\n

There are also some cases in which SMT should not<\/strong> be used:<\/p>\n