Date: Wed, 27 Jun 2018 17:58:20 +0530 From: Steevan Rodrigues <steevanxperia@gmail.com> To: freebsd-hackers@freebsd.org Subject: high CPU usage in FreeBSD for a PCIe card driver Message-ID: <CAKsGTHR9AzX2v%2B%2BDbNCdt7RwxEfw8jKwndXzH9oxQEHvPszo%2Bw@mail.gmail.com>
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[-- Attachment #1 --] Hi I come from Linux background and new to FreeBSD. I am investigating a high CPU usage issue on FreeBSD for PCIe driver of a card . The card can process data at a rate of 30 to 50 Gbps . However, I see very high CPU usage even when I run a single threaded user side application which uses this card . I ran hotkernel script from Dtrace toolkit. A portion of the output is given in the attached file dtraceDiff.txt. Here I see that lock_delay seems to be the reason for high CPU usage. Looks like it comes from mutex locks This driver uses mutex locks ( mtx_lock). The CPU usage is very high on a multicore (Xeon CPU) server node than a dual core (Intel i3) Desktop . It shows 30 to 40 % CPU usage on a Intel i3 ( 2 core 4 threads) and 60 to 70% CPU usage on a Xeon CPU with 12 core (24 threads) for same output data rate . I wonder whether usage of mtx_lock is the cause of high CPU usage ? Any pointers or suggestions welcome. Using FreeBSD 11.1 Release Thanks Steev [-- Attachment #2 --] --------------------------------------------------- CPU usage details on a 12 core 24 thread server PC. part of the perl hotkernel output kernel`free 1314 0.2% kernel`_sx_slock 1415 0.3% kernel`dev_relthread 1435 0.3% kernel`devvn_refthread 1842 0.3% kernel`_mtx_lock_spin_cookie 2059 0.4% kernel`copyin 2164 0.4% kernel`amd64_syscall 2235 0.4% kernel`__mtx_lock_spin_flags 3566 0.6% kernel`bzero 4889 0.9% kernel`__mtx_lock_sleep 9323 1.7% kernel`acpi_cpu_idle 11166 2.0% kernel`pmap_extract 17491 3.1% kernel`spinlock_exit 64850 11.5% kernel`cpu_idle 134617 23.9% kernel`lock_delay 263330 46.8% ------------------------------------------------- CPU usage details on a 2 core 4 thread Intel i3 based Desktop PC. part of the perl hotkernel output kernel`0xffffffff80 558 0.6% kernel`copyout 592 0.6% 0xffffffff822368a3 639 0.7% kernel`amd64_syscall 683 0.7% kernel`__mtx_unlock_flags 728 0.8% kernel`copyin 1311 1.4% kernel`bzero 1434 1.5% kernel`pmap_extract 1615 1.7% kernel`lock_delay 2329 2.4% 0xffffffff822b0b5e 2528 2.6% kernel`spinlock_exit 20950 21.8% kernel`cpu_idle 48124 50.2% ------------------------------------------------------
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