cpu: x64: brgemm convolution blocking: update start_ocb_selection

Author: ankalinin

src/cpu/x64/jit_brgemm_conv_utils.cpp

@@ -1897,7 +1897,12 @@ status_t init_conf(jit_brgemm_conv_conf_t &jcp, cpu_isa_t isa,
         best_brgb.oc_block = min_oc_block;
         brg_blocking_t cur_brgb = zero<decltype(best_brgb)>();
         cur_brgb.get_from_jcp(jcp);
-        auto start_ocb = (is_amx(isa) && jcp.is_os_blocking) ? 2 : 4;
+        const int est_amx_job = div_up(jcp.mb * div_up(jcp.os, 4 * 16)
+                        * jcp.ngroups * div_up(jcp.oc, 4 * 16),
+                nthreads);
+        const bool small_amx_job = est_amx_job < 64 || jcp.oc < 256;
+        auto start_ocb
+                = (is_amx(isa) && jcp.is_os_blocking && small_amx_job) ? 2 : 4;
         if (jcp.wei_plain)
             start_ocb = nstl::min(jcp.ic > 128 ? (jcp.ic > 256 ? 8 : 16) : 32,
                     div_up(jcp.oc, 16));