On Thu, 24 Sep 2020 08:21:47 -0300 Daniel Henrique Barboza <danielhb...@gmail.com> wrote:
> > > On 9/24/20 7:22 AM, Greg Kurz wrote: > > On Wed, 23 Sep 2020 16:34:57 -0300 > > Daniel Henrique Barboza <danielhb...@gmail.com> wrote: > > > >> This patch puts all the pieces together to finally allow user > >> input when defining the NUMA topology of the spapr guest. > >> > >> We have one more kernel restriction to handle in this patch: > >> the associativity array of node 0 must be filled with zeroes > >> [1]. The strategy below ensures that this will happen. > >> > >> spapr_numa_define_associativity_domains() will read the distance > >> (already PAPRified) between the nodes from numa_state and determine > >> the appropriate NUMA level. The NUMA domains, processed in ascending > >> order, are going to be matched via NUMA levels, and the lowest > >> associativity domain value is assigned to that specific level for > >> both. > >> > >> This will create an heuristic where the associativities of the first > >> nodes have higher priority and are re-used in new matches, instead of > >> overwriting them with a new associativity match. This is necessary > >> because neither QEMU, nor the pSeries kernel, supports multiple > >> associativity domains for each resource, meaning that we have to > >> decide which associativity relation is relevant. > >> > >> Ultimately, all of this results in a best effort approximation for > >> the actual NUMA distances the user input in the command line. Given > >> the nature of how PAPR itself interprets NUMA distances versus the > >> expectations risen by how ACPI SLIT works, there might be better > >> algorithms but, in the end, it'll also result in another way to > >> approximate what the user really wanted. > >> > >> To keep this commit message no longer than it already is, the next > >> patch will update the existing documentation in ppc-spapr-numa.rst > >> with more in depth details and design considerations/drawbacks. > >> > >> [1] > >> https://lore.kernel.org/linuxppc-dev/5e8fbea3-8faf-0951-172a-b41a2138f...@gmail.com/ > >> > >> Signed-off-by: Daniel Henrique Barboza <danielhb...@gmail.com> > >> --- > >> hw/ppc/spapr_numa.c | 81 ++++++++++++++++++++++++++++++++++++++++++++- > >> 1 file changed, 80 insertions(+), 1 deletion(-) > >> > >> diff --git a/hw/ppc/spapr_numa.c b/hw/ppc/spapr_numa.c > >> index 688391278e..c84f77cda7 100644 > >> --- a/hw/ppc/spapr_numa.c > >> +++ b/hw/ppc/spapr_numa.c > >> @@ -80,12 +80,79 @@ static void spapr_numa_PAPRify_distances(MachineState > >> *ms) > >> } > >> } > >> > >> +static uint8_t spapr_numa_get_NUMA_level(uint8_t distance) > > > > The funky naming doesn't improve clarity IMHO. I'd rather make > > it lowercase only. > > > >> +{ > >> + uint8_t numa_level; > >> + > >> + switch (distance) { > >> + case 20: > >> + numa_level = 0x3; > >> + break; > >> + case 40: > >> + numa_level = 0x2; > >> + break; > >> + case 80: > >> + numa_level = 0x1; > >> + break; > >> + default: > >> + numa_level = 0; > > > > Hmm... same level for distances 10 and 160 ? Is this correct ? > > > This will never be called with distance = 10 because we won't > evaluate distance between the node to itself. But I'll put a > 'case 10:' clause there that does nothing to make it clearer. > You should make it g_assert_not_reached() in this case. > > > DHB > > > > >> + } > >> + > >> + return numa_level; > >> +} > >> + > >> +static void spapr_numa_define_associativity_domains(SpaprMachineState > >> *spapr, > >> + MachineState *ms) > > > > Passing ms seems to indicate that it could have a different value than > > spapr, > > which is certainly no true. > > > > I'd rather make it a local variable: > > > > MachineState *ms = MACHINE(spapr); > > > > This is an slow path : we don't really care to do dynamic type checking > > multiple times. > > > >> +{ > >> + int src, dst; > >> + int nb_numa_nodes = ms->numa_state->num_nodes; > >> + NodeInfo *numa_info = ms->numa_state->nodes; > >> + > >> + for (src = 0; src < nb_numa_nodes; src++) { > >> + for (dst = src; dst < nb_numa_nodes; dst++) { > >> + /* > >> + * This is how the associativity domain between A and B > >> + * is calculated: > >> + * > >> + * - get the distance between them > >> + * - get the correspondent NUMA level for this distance > >> + * - the arrays were initialized with their own numa_ids, > >> + * and we're calculating the distance in node_id ascending > >> order, > >> + * starting from node 0. This will have a cascade effect in > >> the > >> + * algorithm because the associativity domains that node 0 > >> defines > >> + * will be carried over to the other nodes, and node 1 > >> + * associativities will be carried over unless there's > >> already a > >> + * node 0 associativity assigned, and so on. This happens > >> because > >> + * we'll assign the lowest value of assoc_src and assoc_dst > >> to be > >> + * the associativity domain of both, for the given NUMA level. > >> + * > >> + * The PPC kernel expects the associativity domains of node 0 > >> to > >> + * be always 0, and this algorithm will grant that by default. > >> + */ > >> + uint8_t distance = numa_info[src].distance[dst]; > >> + uint8_t n_level = spapr_numa_get_NUMA_level(distance); > >> + uint32_t assoc_src, assoc_dst; > >> + > >> + assoc_src = > >> be32_to_cpu(spapr->numa_assoc_array[src][n_level]); > >> + assoc_dst = > >> be32_to_cpu(spapr->numa_assoc_array[dst][n_level]); > >> + > >> + if (assoc_src < assoc_dst) { > >> + spapr->numa_assoc_array[dst][n_level] = > >> cpu_to_be32(assoc_src); > >> + } else { > >> + spapr->numa_assoc_array[src][n_level] = > >> cpu_to_be32(assoc_dst); > >> + } > >> + } > >> + } > >> + > >> +} > >> + > >> void spapr_numa_associativity_init(SpaprMachineState *spapr, > >> MachineState *machine) > >> { > >> SpaprMachineClass *smc = SPAPR_MACHINE_GET_CLASS(spapr); > >> int nb_numa_nodes = machine->numa_state->num_nodes; > >> int i, j, max_nodes_with_gpus; > >> + bool using_legacy_numa = spapr_machine_using_legacy_numa(spapr); > >> > >> /* > >> * For all associativity arrays: first position is the size, > >> @@ -99,6 +166,17 @@ void spapr_numa_associativity_init(SpaprMachineState > >> *spapr, > >> for (i = 0; i < nb_numa_nodes; i++) { > >> spapr->numa_assoc_array[i][0] = > >> cpu_to_be32(MAX_DISTANCE_REF_POINTS); > >> spapr->numa_assoc_array[i][MAX_DISTANCE_REF_POINTS] = > >> cpu_to_be32(i); > >> + > >> + /* > >> + * Fill all associativity domains of the node with node_id. > >> + * This is required because the kernel makes valid associativity > > > > It would be appreciated to have an URL to the corresponding code in the > > changelog. > > > >> + * matches with the zeroes if we leave the matrix unitialized. > >> + */ > >> + if (!using_legacy_numa) { > >> + for (j = 1; j < MAX_DISTANCE_REF_POINTS; j++) { > >> + spapr->numa_assoc_array[i][j] = cpu_to_be32(i); > >> + } > >> + } > >> } > >> > >> /* > >> @@ -128,7 +206,7 @@ void spapr_numa_associativity_init(SpaprMachineState > >> *spapr, > >> * 1 NUMA node) will not benefit from anything we're going to do > >> * after this point. > >> */ > >> - if (spapr_machine_using_legacy_numa(spapr)) { > >> + if (using_legacy_numa) { > >> return; > >> } > >> > >> @@ -139,6 +217,7 @@ void spapr_numa_associativity_init(SpaprMachineState > >> *spapr, > >> } > >> > >> spapr_numa_PAPRify_distances(machine); > >> + spapr_numa_define_associativity_domains(spapr, machine); > >> } > >> > >> void spapr_numa_write_associativity_dt(SpaprMachineState *spapr, void > >> *fdt, > >