[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [PATCH v6 01/15] xen/common: add cache coloring common code
Last Level Cache (LLC) coloring allows to partition the cache in smaller chunks called cache colors. Since not all architectures can actually implement it, add a HAS_LLC_COLORING Kconfig and put other options under xen/arch. LLC colors are a property of the domain, so the domain struct has to be extended. Based on original work from: Luca Miccio <lucmiccio@xxxxxxxxx> Signed-off-by: Carlo Nonato <carlo.nonato@xxxxxxxxxxxxxxx> Signed-off-by: Marco Solieri <marco.solieri@xxxxxxxxxxxxxxx> --- v6: - moved almost all code in common - moved documentation in this patch - reintroduced range for CONFIG_NR_LLC_COLORS - reintroduced some stub functions to reduce the number of checks on llc_coloring_enabled - moved domain_llc_coloring_free() in same patch where allocation happens - turned "d->llc_colors" to pointer-to-const - llc_coloring_init() now returns void and panics if errors are found v5: - used - instead of _ for filenames - removed domain_create_llc_colored() - removed stub functions - coloring domain fields are now #ifdef protected v4: - Kconfig options moved to xen/arch - removed range for CONFIG_NR_LLC_COLORS - added "llc_coloring_enabled" global to later implement the boot-time switch - added domain_create_llc_colored() to be able to pass colors - added is_domain_llc_colored() macro --- docs/misc/cache-coloring.rst | 87 +++++++++++++++++++++++++++++++ docs/misc/xen-command-line.pandoc | 27 ++++++++++ xen/arch/Kconfig | 17 ++++++ xen/common/Kconfig | 3 ++ xen/common/Makefile | 1 + xen/common/keyhandler.c | 3 ++ xen/common/llc-coloring.c | 87 +++++++++++++++++++++++++++++++ xen/include/xen/llc-coloring.h | 38 ++++++++++++++ xen/include/xen/sched.h | 5 ++ 9 files changed, 268 insertions(+) create mode 100644 docs/misc/cache-coloring.rst create mode 100644 xen/common/llc-coloring.c create mode 100644 xen/include/xen/llc-coloring.h diff --git a/docs/misc/cache-coloring.rst b/docs/misc/cache-coloring.rst new file mode 100644 index 0000000000..9fe01e99e1 --- /dev/null +++ b/docs/misc/cache-coloring.rst @@ -0,0 +1,87 @@ +Xen cache coloring user guide +============================= + +The cache coloring support in Xen allows to reserve Last Level Cache (LLC) +partitions for Dom0, DomUs and Xen itself. Currently only ARM64 is supported. + +To compile LLC coloring support set ``CONFIG_LLC_COLORING=y``. + +If needed, change the maximum number of colors with +``CONFIG_NR_LLC_COLORS=<n>``. + +Compile Xen and the toolstack and then configure it via +`Command line parameters`_. + +Background +********** + +Cache hierarchy of a modern multi-core CPU typically has first levels dedicated +to each core (hence using multiple cache units), while the last level is shared +among all of them. Such configuration implies that memory operations on one +core (e.g. running a DomU) are able to generate interference on another core +(e.g .hosting another DomU). Cache coloring allows eliminating this +mutual interference, and thus guaranteeing higher and more predictable +performances for memory accesses. +The key concept underlying cache coloring is a fragmentation of the memory +space into a set of sub-spaces called colors that are mapped to disjoint cache +partitions. Technically, the whole memory space is first divided into a number +of subsequent regions. Then each region is in turn divided into a number of +subsequent sub-colors. The generic i-th color is then obtained by all the +i-th sub-colors in each region. + +:: + + Region j Region j+1 + ..................... ............ + . . . + . . + _ _ _______________ _ _____________________ _ _ + | | | | | | | + | c_0 | c_1 | | c_n | c_0 | c_1 | + _ _ _|_____|_____|_ _ _|_____|_____|_____|_ _ _ + : : + : :... ... . + : color 0 + :........................... ... . + : + . . ..................................: + +There are two pragmatic lesson to be learnt. + +1. If one wants to avoid cache interference between two domains, different + colors needs to be used for their memory. + +2. Color assignment must privilege contiguity in the partitioning. E.g., + assigning colors (0,1) to domain I and (2,3) to domain J is better than + assigning colors (0,2) to I and (1,3) to J. + +How to compute the number of colors +*********************************** + +To compute the number of available colors for a specific platform, the size of +an LLC way and the page size used by Xen must be known. The first parameter can +be found in the processor manual or can be also computed dividing the total +cache size by the number of its ways. The second parameter is the minimum +amount of memory that can be mapped by the hypervisor, thus dividing the way +size by the page size, the number of total cache partitions is found. So for +example, an Arm Cortex-A53 with a 16-ways associative 1 MiB LLC, can isolate up +to 16 colors when pages are 4 KiB in size. + +Cache layout is probed automatically by looking at the CLIDR_EL1 arm register. +This means that other system caches that aren't visible there, are ignored. +The possibility of manually setting the way size is left to the user to overcome +failing situations or for debugging/testing purposes. See +`Command line parameters`_ for more information on that. + +Command line parameters +*********************** + +More specific documentation is available at `docs/misc/xen-command-line.pandoc`. + ++----------------------+-------------------------------+ +| **Parameter** | **Description** | ++----------------------+-------------------------------+ +| ``llc-coloring`` | enable coloring at runtime | ++----------------------+-------------------------------+ +| ``llc-way-size`` | set the LLC way size | ++----------------------+-------------------------------+ diff --git a/docs/misc/xen-command-line.pandoc b/docs/misc/xen-command-line.pandoc index 8e65f8bd18..11f9f209d1 100644 --- a/docs/misc/xen-command-line.pandoc +++ b/docs/misc/xen-command-line.pandoc @@ -1713,6 +1713,33 @@ This option is intended for debugging purposes only. Enable MSR_DEBUGCTL.LBR in hypervisor context to be able to dump the Last Interrupt/Exception To/From record with other registers. +### llc-coloring +> `= <boolean>` + +> Default: `false` + +Flag to enable or disable LLC coloring support at runtime. This options is +available only when `CONFIG_LLC_COLORING` is enabled. See the general +cache coloring documentation for more info. + +### llc-way-size +> `= <size>` + +> Default: `Obtained from the hardware` + +Specify the way size of the Last Level Cache. This options is available only +when `CONFIG_LLC_COLORING` is enabled. It is an optional, expert-only parameter +and it is used to calculate the number of available LLC colors on the platform. +It can be obtained by dividing the total LLC size by the number of its +associative ways. +By default, the value is automatically computed by probing the hardware, but in +case of specific needs, it can be manually set. Those include failing probing +and debugging/testing purposes so that it's possibile to emulate platforms with +different number of supported colors. +An important detail to highlight is that the current implementation of the +cache coloring technique requires the number of colors to be a power of 2, and +consequently, also the LLC way size must be so. + ### lock-depth-size > `= <integer>` diff --git a/xen/arch/Kconfig b/xen/arch/Kconfig index 67ba38f32f..c1157bcbcb 100644 --- a/xen/arch/Kconfig +++ b/xen/arch/Kconfig @@ -31,3 +31,20 @@ config NR_NUMA_NODES associated with multiple-nodes management. It is the upper bound of the number of NUMA nodes that the scheduler, memory allocation and other NUMA-aware components can handle. + +config LLC_COLORING + bool "Last Level Cache (LLC) coloring" if EXPERT + depends on HAS_LLC_COLORING + +config NR_LLC_COLORS + int "Maximum number of LLC colors" + range 2 1024 + default 128 + depends on LLC_COLORING + help + Controls the build-time size of various arrays associated with LLC + coloring. Refer to cache coloring documentation for how to compute the + number of colors supported by the platform. This is only an upper + bound. The runtime value is autocomputed or manually set via cmdline. + The default value corresponds to an 8 MiB 16-ways LLC, which should be + more than what needed in the general case. diff --git a/xen/common/Kconfig b/xen/common/Kconfig index 310ad4229c..e383f09d97 100644 --- a/xen/common/Kconfig +++ b/xen/common/Kconfig @@ -71,6 +71,9 @@ config HAS_IOPORTS config HAS_KEXEC bool +config HAS_LLC_COLORING + bool + config HAS_PMAP bool diff --git a/xen/common/Makefile b/xen/common/Makefile index 69d6aa626c..409cc53e2a 100644 --- a/xen/common/Makefile +++ b/xen/common/Makefile @@ -24,6 +24,7 @@ obj-y += keyhandler.o obj-$(CONFIG_KEXEC) += kexec.o obj-$(CONFIG_KEXEC) += kimage.o obj-$(CONFIG_LIVEPATCH) += livepatch.o livepatch_elf.o +obj-$(CONFIG_LLC_COLORING) += llc-coloring.o obj-$(CONFIG_MEM_ACCESS) += mem_access.o obj-y += memory.o obj-y += multicall.o diff --git a/xen/common/keyhandler.c b/xen/common/keyhandler.c index 99a2d72a02..8d90b613f7 100644 --- a/xen/common/keyhandler.c +++ b/xen/common/keyhandler.c @@ -6,6 +6,7 @@ #include <xen/debugger.h> #include <xen/delay.h> #include <xen/keyhandler.h> +#include <xen/llc-coloring.h> #include <xen/param.h> #include <xen/shutdown.h> #include <xen/event.h> @@ -307,6 +308,8 @@ static void cf_check dump_domains(unsigned char key) arch_dump_domain_info(d); + domain_dump_llc_colors(d); + rangeset_domain_printk(d); dump_pageframe_info(d); diff --git a/xen/common/llc-coloring.c b/xen/common/llc-coloring.c new file mode 100644 index 0000000000..10729e70c1 --- /dev/null +++ b/xen/common/llc-coloring.c @@ -0,0 +1,87 @@ +/* SPDX-License-Identifier: GPL-2.0-only */ +/* + * Last Level Cache (LLC) coloring common code + * + * Copyright (C) 2022 Xilinx Inc. + */ +#include <xen/keyhandler.h> +#include <xen/llc-coloring.h> +#include <xen/param.h> + +bool __ro_after_init llc_coloring_enabled; +boolean_param("llc-coloring", llc_coloring_enabled); + +/* Size of an LLC way */ +static unsigned int __ro_after_init llc_way_size; +size_param("llc-way-size", llc_way_size); +/* Number of colors available in the LLC */ +static unsigned int __ro_after_init max_nr_colors = CONFIG_NR_LLC_COLORS; + +static void print_colors(const unsigned int *colors, unsigned int num_colors) +{ + unsigned int i; + + printk("{ "); + for ( i = 0; i < num_colors; i++ ) { + unsigned int start = colors[i], end = colors[i]; + + printk("%u", start); + + for ( ; + i < num_colors - 1 && colors[i] + 1 == colors[i + 1]; + i++, end++ ); + + if ( start != end ) + printk("-%u", end); + + if ( i < num_colors - 1 ) + printk(", "); + } + printk(" }\n"); +} + +static void dump_coloring_info(unsigned char key) +{ + printk("'%c' pressed -> dumping LLC coloring general info\n", key); + printk("LLC way size: %u KiB\n", llc_way_size >> 10); + printk("Number of LLC colors supported: %u\n", max_nr_colors); +} + +void __init llc_coloring_init(void) +{ + if ( !llc_way_size && !(llc_way_size = get_llc_way_size()) ) + panic("Probed LLC coloring way size is 0 and no custom value found\n"); + + /* + * The maximum number of colors must be a power of 2 in order to correctly + * map them to bits of an address, so also the LLC way size must be so. + */ + if ( llc_way_size & (llc_way_size - 1) ) + panic("LLC coloring way size (%u) isn't a power of 2\n", llc_way_size); + + max_nr_colors = llc_way_size >> PAGE_SHIFT; + + if ( max_nr_colors < 2 || max_nr_colors > CONFIG_NR_LLC_COLORS ) + panic("Number of LLC colors (%u) not in range [2, %u]\n", + max_nr_colors, CONFIG_NR_LLC_COLORS); + + register_keyhandler('K', dump_coloring_info, "dump LLC coloring info", 1); + + arch_llc_coloring_init(); +} + +void domain_dump_llc_colors(const struct domain *d) +{ + printk("Domain %pd has %u LLC colors: ", d, d->num_llc_colors); + print_colors(d->llc_colors, d->num_llc_colors); +} + +/* + * Local variables: + * mode: C + * c-file-style: "BSD" + * c-basic-offset: 4 + * tab-width: 4 + * indent-tabs-mode: nil + * End: + */ diff --git a/xen/include/xen/llc-coloring.h b/xen/include/xen/llc-coloring.h new file mode 100644 index 0000000000..5e12eb426f --- /dev/null +++ b/xen/include/xen/llc-coloring.h @@ -0,0 +1,38 @@ +/* SPDX-License-Identifier: GPL-2.0-only */ +/* + * Last Level Cache (LLC) coloring common header + * + * Copyright (C) 2022 Xilinx Inc. + */ +#ifndef __COLORING_H__ +#define __COLORING_H__ + +#include <xen/sched.h> +#include <public/domctl.h> + +#ifdef CONFIG_LLC_COLORING +extern bool llc_coloring_enabled; + +void llc_coloring_init(void); +void domain_dump_llc_colors(const struct domain *d); +#else +#define llc_coloring_enabled false + +static inline void llc_coloring_init(void) {} +static inline void domain_dump_llc_colors(const struct domain *d) {} +#endif + +unsigned int get_llc_way_size(void); +void arch_llc_coloring_init(void); + +#endif /* __COLORING_H__ */ + +/* + * Local variables: + * mode: C + * c-file-style: "BSD" + * c-basic-offset: 4 + * tab-width: 4 + * indent-tabs-mode: nil + * End: + */ diff --git a/xen/include/xen/sched.h b/xen/include/xen/sched.h index 9da91e0e62..8df0f29335 100644 --- a/xen/include/xen/sched.h +++ b/xen/include/xen/sched.h @@ -626,6 +626,11 @@ struct domain /* Holding CDF_* constant. Internal flags for domain creation. */ unsigned int cdf; + +#ifdef CONFIG_LLC_COLORING + unsigned const int *llc_colors; + unsigned int num_llc_colors; +#endif }; static inline struct page_list_head *page_to_list( -- 2.34.1
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