Hi Gautham,
On 8/21/2025 12:02 AM, Gautham R. Shenoy wrote:
Hello Babu,
On Tue, Aug 05, 2025 at 06:30:26PM -0500, Babu Moger wrote:
"io_alloc" feature in resctrl enables direct insertion of data from I/O
devices into the cache.
On AMD systems, when io_alloc is enabled, the highest CLOSID is reserved
exclusively for I/O allocation traffic and is no longer available for
general CPU cache allocation. Users are encouraged to enable it only when
running workloads that can benefit from this functionality.
Since CLOSIDs are managed by resctrl fs, it is least invasive to make the
"io_alloc is supported by maximum supported CLOSID" part of the initial
resctrl fs support for io_alloc. Take care not to expose this use of CLOSID
for io_alloc to user space so that this is not required from other
architectures that may support io_alloc differently in the future.
Introduce user interface to enable/disable io_alloc feature.
Signed-off-by: Babu Moger <babu.moger@xxxxxxx>
[..snip..]
+ssize_t resctrl_io_alloc_write(struct kernfs_open_file *of, char *buf,
+ size_t nbytes, loff_t off)
+{
+ struct resctrl_schema *s = rdt_kn_parent_priv(of->kn);
+ struct rdt_resource *r = s->res;
+ char const *grp_name;
+ u32 io_alloc_closid;
+ bool enable;
+ int ret;
+
+ ret = kstrtobool(buf, &enable);
+ if (ret)
+ return ret;
+
+ cpus_read_lock();
+ mutex_lock(&rdtgroup_mutex);
+
+ rdt_last_cmd_clear();
+
+ if (!r->cache.io_alloc_capable) {
+ rdt_last_cmd_printf("io_alloc is not supported on %s\n", s->name);
+ ret = -ENODEV;
+ goto out_unlock;
+ }
+
+ io_alloc_closid = resctrl_io_alloc_closid(r);
+ if (!resctrl_io_alloc_closid_supported(io_alloc_closid)) {
+ rdt_last_cmd_printf("io_alloc CLOSID (ctrl_hw_id) %d is not available\n",
+ io_alloc_closid);
+ ret = -EINVAL;
+ goto out_unlock;
+ }
+
+ /* If the feature is already up to date, no action is needed. */
+ if (resctrl_arch_get_io_alloc_enabled(r) == enable)
+ goto out_unlock;
Does it make sense to move this check before calling resctrl_io_alloc_closid(r) ?
Sure. We can do that.
Thanks
Babu
+
+ if (enable) {
+ if (!closid_alloc_fixed(io_alloc_closid)) {
+ grp_name = rdtgroup_name_by_closid(io_alloc_closid);
+ WARN_ON_ONCE(!grp_name);
+ rdt_last_cmd_printf("CLOSID (ctrl_hw_id) %d for io_alloc is used by %s group\n",
+ io_alloc_closid, grp_name ? grp_name : "another");
+ ret = -ENOSPC;
+ goto out_unlock;
+ }
+
+ ret = resctrl_io_alloc_init_cbm(s, io_alloc_closid);
+ if (ret) {
+ rdt_last_cmd_puts("Failed to initialize io_alloc allocations\n");
+ closid_free(io_alloc_closid);
+ goto out_unlock;
+ }
+ } else {
+ closid_free(io_alloc_closid);
+ }
+
+ ret = resctrl_arch_io_alloc_enable(r, enable);
+
+out_unlock:
+ mutex_unlock(&rdtgroup_mutex);
+ cpus_read_unlock();
+
+ return ret ?: nbytes;
+}
[..snip..]
