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Before this patch the driver had one CQ database protected via one spinlock, this spinlock is meant to synchronize between CQ adding/removing and CQ IRQ interrupt handling. On a system with large number of CPUs and on a work load that requires lots of interrupts, this global spinlock becomes a very nasty hotspot and introduces a contention between the active cores, which will significantly hurt performance and becomes a bottleneck that prevents seamless cpu scaling. To solve this we simply move the CQ database and its spinlock to be per EQ (IRQ), thus per core. Tested with: system: 2 sockets, 14 cores per socket, hyperthreading, 2x14x2=56 cores netperf command: ./super_netperf 200 -P 0 -t TCP_RR -H <server> -l 30 -- -r 300,300 -o -s 1M,1M -S 1M,1M WITHOUT THIS PATCH: Average: CPU %usr %nice %sys %iowait %irq %soft %steal %guest %gnice %idle Average: all 4.32 0.00 36.15 0.09 0.00 34.02 0.00 0.00 0.00 25.41 Samples: 2M of event 'cycles:pp', Event count (approx.): 1554616897271 Overhead Command Shared Object Symbol + 14.28% swapper [kernel.vmlinux] [k] intel_idle + 12.25% swapper [kernel.vmlinux] [k] queued_spin_lock_slowpath + 10.29% netserver [kernel.vmlinux] [k] queued_spin_lock_slowpath + 1.32% netserver [kernel.vmlinux] [k] mlx5e_xmit WITH THIS PATCH: Average: CPU %usr %nice %sys %iowait %irq %soft %steal %guest %gnice %idle Average: all 4.27 0.00 34.31 0.01 0.00 18.71 0.00 0.00 0.00 42.69 Samples: 2M of event 'cycles:pp', Event count (approx.): 1498132937483 Overhead Command Shared Object Symbol + 23.33% swapper [kernel.vmlinux] [k] intel_idle + 1.69% netserver [kernel.vmlinux] [k] mlx5e_xmit Tested-by: Song Liu <songliubraving@fb.com> Signed-off-by: Saeed Mahameed <saeedm@mellanox.com> Reviewed-by: Gal Pressman <galp@mellanox.com> |
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Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.