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Date:   Wed, 18 Nov 2020 07:38:58 -0800
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Subject: [RFC PATCH v3 12/61] e2fsck: split groups to different threads
From:   Saranya Muruganandam <saranyamohan@google.com>
To:     linux-ext4@vger.kernel.org, tytso@mit.edu
Cc:     adilger.kernel@dilger.ca, Li Xi <lixi@ddn.com>,
        Wang Shilong <wshilong@ddn.com>,
        Saranya Muruganandam <saranyamohan@google.com>
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From: Li Xi <lixi@ddn.com>

The start/end groups of a thread is calculated according to the
thread number. But still, only one thread is used to check.

Signed-off-by: Li Xi <lixi@ddn.com>
Signed-off-by: Wang Shilong <wshilong@ddn.com>
Signed-off-by: Saranya Muruganandam <saranyamohan@google.com>
---
 e2fsck/pass1.c | 23 +++++++++++++++++------
 1 file changed, 17 insertions(+), 6 deletions(-)

diff --git a/e2fsck/pass1.c b/e2fsck/pass1.c
index bb32511f..fd354529 100644
--- a/e2fsck/pass1.c
+++ b/e2fsck/pass1.c
@@ -2232,13 +2232,14 @@ static int e2fsck_pass1_merge_fs(ext2_filsys dest, ext2_filsys src)
 }
 
 static errcode_t e2fsck_pass1_thread_prepare(e2fsck_t global_ctx, e2fsck_t *thread_ctx,
-					     int thread_index)
+					     int thread_index, int num_threads)
 {
 	errcode_t		retval;
 	e2fsck_t		thread_context;
 	ext2_filsys		thread_fs;
 	ext2_filsys		global_fs = global_ctx->fs;
 	struct e2fsck_thread	*tinfo;
+	dgrp_t			average_group;
 
 	assert(global_ctx->inode_used_map == NULL);
 	assert(global_ctx->inode_dir_map == NULL);
@@ -2278,11 +2279,20 @@ static errcode_t e2fsck_pass1_thread_prepare(e2fsck_t global_ctx, e2fsck_t *thre
 	thread_context->thread_info.et_thread_index = thread_index;
 	set_up_logging(thread_context);
 
-	assert(thread_index == 0);
+	/*
+	 * Distribute work to multiple threads:
+	 * Each thread work on fs->group_desc_count / nthread groups.
+	 */
 	tinfo = &thread_context->thread_info;
-	tinfo->et_group_start = 0;
-	tinfo->et_group_next = 0;
-	tinfo->et_group_end = thread_fs->group_desc_count;
+	average_group = thread_fs->group_desc_count / num_threads;
+	if (average_group == 0)
+		average_group = 1;
+	tinfo->et_group_start = average_group * thread_index;
+	if (thread_index == num_threads - 1)
+		tinfo->et_group_end = thread_fs->group_desc_count;
+	else
+		tinfo->et_group_end = average_group * (thread_index + 1);
+	tinfo->et_group_next = tinfo->et_group_start;
 
 	thread_context->fs = thread_fs;
 	*thread_ctx = thread_context;
@@ -2506,7 +2516,8 @@ static int e2fsck_pass1_threads_start(struct e2fsck_thread_info **pinfo,
 	for (i = 0; i < num_threads; i++) {
 		tmp_pinfo = &infos[i];
 		tmp_pinfo->eti_thread_index = i;
-		retval = e2fsck_pass1_thread_prepare(global_ctx, &thread_ctx, i);
+		retval = e2fsck_pass1_thread_prepare(global_ctx, &thread_ctx,
+						     i, num_threads);
 		if (retval) {
 			com_err(global_ctx->program_name, retval,
 				_("while preparing pass1 thread\n"));
-- 
2.29.2.299.gdc1121823c-goog