Anup Patel 65d4b9c530 RISC-V: Implement ASID allocator ... Currently, we do local TLB flush on every MM switch. This is very harsh on performance because we are forcing page table walks after every MM switch. This patch implements ASID allocator for assigning an ASID to a MM context. The number of ASIDs are limited in HW so we create a logical entity named CONTEXTID for assigning to MM context. The lower bits of CONTEXTID are ASID and upper bits are VERSION number. The number of usable ASID bits supported by HW are detected at boot-time by writing 1s to ASID bits in SATP CSR. We allocate new CONTEXTID on first MM switch for a MM context where the ASID is allocated from an ASID bitmap and VERSION is provide by an atomic counter. At time of allocating new CONTEXTID, if we run out of available ASIDs then: 1. We flush the ASID bitmap 2. Increment current VERSION atomic counter 3. Re-allocate ASID from ASID bitmap 4. Flush TLB on all CPUs 5. Try CONTEXTID re-assignment on all CPUs Please note that we don't use ASID #0 because it is used at boot-time by all CPUs for initial MM context. Also, newly created context is always assigned CONTEXTID #0 (i.e. VERSION #0 and ASID #0) which is an invalid context in our implementation. Using above approach, we have virtually infinite CONTEXTIDs on-top-of limited number of HW ASIDs. This approach is inspired from ASID allocator used for Linux ARM/ARM64 but we have adapted it for RISC-V. Overall, this ASID allocator helps us reduce rate of local TLB flushes on every CPU thereby increasing performance. This patch is tested on QEMU virt machine, Spike and SiFive Unleashed board. On QEMU virt machine, we see some (3-5% approx) performance improvement with SW emulated TLBs provided by QEMU. Unfortunately, the ASID bits of the SATP CSR are not implemented on Spike and SiFive Unleashed board so we don't see any change in performance. On real HW having all ASID bits implemented, the performance gains will be much more due improved sharing of TLB among different processes. Signed-off-by: Anup Patel <anup.patel@wdc.com> Reviewed-by: Palmer Dabbelt <palmerdabbelt@google.com> Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>		2021-02-18 23:18:06 -08:00
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boot	riscv: Fix Canaan Kendryte K210 device tree	2021-01-14 15:08:47 -08:00
configs	riscv: Use vendor name for K210 SoC support	2021-01-14 15:08:46 -08:00
include	RISC-V: Implement ASID allocator	2021-02-18 23:18:06 -08:00
kernel	RISC-V: probes: Treat the instruction stream as host-endian	2021-02-18 23:18:02 -08:00
lib	riscv: Add support for function error injection	2021-01-14 15:09:09 -08:00
mm	RISC-V: Implement ASID allocator	2021-02-18 23:18:06 -08:00
net	treewide: Use fallthrough pseudo-keyword	2020-08-23 17:36:59 -05:00
Kbuild	riscv: Allow device trees to be built into the kernel	2020-05-18 11:38:05 -07:00
Kconfig	riscv/kasan: add KASAN_VMALLOC support	2021-02-18 23:17:59 -08:00
Kconfig.debug	RISC-V: Remove EARLY_PRINTK support	2018-12-17 10:23:46 -08:00
Kconfig.socs	pinctrl: Add RISC-V Canaan Kendryte K210 FPIOA driver	2021-02-18 23:18:01 -08:00
Makefile	riscv: Enable per-task stack canaries	2021-01-14 15:09:10 -08:00