From 0318589c8bc3de6132af7f7d197295f58d89424b Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Christian=20G=C3=B6ttsche?= <cgzones@googlemail.com>
Date: Sun, 5 Nov 2023 17:31:16 +0100
Subject: Linux: scan GPU based on previous activity

Instead of ignoring the standard file descriptors 0, 1 and 2 scan for
GPU usage of a process only if that process had activity last cycle or
its last scan was more than five seconds ago.
---
 linux/GPU.c          | 17 +++++++++++------
 linux/LinuxProcess.h |  2 ++
 2 files changed, 13 insertions(+), 6 deletions(-)

diff --git a/linux/GPU.c b/linux/GPU.c
index 7b6ef886..37d5d7c4 100644
--- a/linux/GPU.c
+++ b/linux/GPU.c
@@ -79,11 +79,19 @@ static void update_machine_gpu(LinuxProcessTable* lpt, unsigned long long int ti
  * https://www.kernel.org/doc/html/latest/gpu/drm-usage-stats.html
  */
 void GPU_readProcessData(LinuxProcessTable* lpt, LinuxProcess* lp, openat_arg_t procFd) {
+   const Machine* host = lp->super.super.host;
    int fdinfoFd = -1;
    DIR* fdinfoDir = NULL;
    ClientInfo* parsed_ids = NULL;
    unsigned long long int new_gpu_time = 0;
 
+   /* check only if active in last check or last scan was more than 5s ago */
+   if (lp->gpu_activityMs != 0 && host->monotonicMs - lp->gpu_activityMs < 5000) {
+      lp->gpu_percent = 0.0f;
+      return;
+   }
+   lp->gpu_activityMs = host->monotonicMs;
+
    fdinfoFd = Compat_openat(procFd, "fdinfo", O_RDONLY | O_NOFOLLOW | O_DIRECTORY | O_CLOEXEC);
    if (fdinfoFd == -1)
       goto out;
@@ -108,11 +116,7 @@ void GPU_readProcessData(LinuxProcessTable* lpt, LinuxProcess* lp, openat_arg_t
          break;
       const char* ename = entry->d_name;
 
-      if (String_eq(ename, ".") ||
-          String_eq(ename, "..") ||
-          String_eq(ename, "0") ||
-          String_eq(ename, "1") ||
-          String_eq(ename, "2"))
+      if (ename[0] == '.' && (ename[1] == '\0' || (ename[1] == '.' && ename[2] == '\0')))
          continue;
 
       char buffer[4096];
@@ -211,7 +215,6 @@ void GPU_readProcessData(LinuxProcessTable* lpt, LinuxProcess* lp, openat_arg_t
    } /* finished parsing fdinfo entries */
 
    if (new_gpu_time > 0) {
-      const Machine* host = lp->super.super.host;
       unsigned long long int gputimeDelta;
       uint64_t monotonicTimeDelta;
 
@@ -220,6 +223,8 @@ void GPU_readProcessData(LinuxProcessTable* lpt, LinuxProcess* lp, openat_arg_t
       gputimeDelta = saturatingSub(new_gpu_time, lp->gpu_time);
       monotonicTimeDelta = host->monotonicMs - host->prevMonotonicMs;
       lp->gpu_percent = 100.0f * gputimeDelta / (1000 * 1000) / monotonicTimeDelta;
+
+      lp->gpu_activityMs = 0;
    } else
       lp->gpu_percent = 0.0f;
 
diff --git a/linux/LinuxProcess.h b/linux/LinuxProcess.h
index cc515f5f..5a1e6272 100644
--- a/linux/LinuxProcess.h
+++ b/linux/LinuxProcess.h
@@ -111,6 +111,8 @@ typedef struct LinuxProcess_ {
    unsigned long long int gpu_time;
    /* GPU utilization in percent */
    float gpu_percent;
+   /* Activity of GPU: 0 if active, otherwise time of last scan in milliseconds */
+   uint64_t gpu_activityMs;
 
    /* Autogroup scheduling (CFS) information */
    long int autogroup_id;
-- 
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